diff --git a/lib/simple_ui/builder.lua b/lib/simple_ui/builder.lua
new file mode 100644
index 0000000..096d0d8
--- /dev/null
+++ b/lib/simple_ui/builder.lua
@@ -0,0 +1,77 @@
+--- Объект, который отвечает за работу с элементами интерфейса одного экрана
+--- @class UIBuilder
+--- @field private _cache UIElement[]
+--- @field elementTree UIElement
+local builder = {}
+builder.__index = builder
+
+local function new(elementTree)
+    local l = {}
+    l.elementTree = elementTree
+    l._cache = {}
+
+    setmetatable(l, builder)
+    return l
+end
+
+--- @param element? UIElement
+--- @private
+function builder:_get(element)
+    if not element then return nil end
+
+    local key = builder:_makeKey(element)
+    if not key then return element end
+
+    local cached = self._cache[key]
+    if cached then return cached end
+
+    self._cache[key] = element
+    return element
+end
+
+--- @param element UIElement
+--- @private
+function builder:_makeKey(element)
+    if not element.key then return nil end
+    if type(element.key) == "string" then return element.key end
+    element.key = element.type .. "<" .. tostring(element.key) .. ">"
+    return element.key
+end
+
+--- @private
+function builder:build_step(cur)
+    if not cur then return end
+    if cur.build then
+        cur.child = self:_get(cur:build())
+        self:build_step(cur.child)
+    elseif cur.children then
+        for _, child in ipairs(cur.children) do
+            self:build_step(self:_get(child))
+        end
+    else
+        cur.child = self:_get(cur.child)
+        self:build_step(cur.child)
+    end
+end
+
+--- Этот метод раскрывает всех отложенных (через build) детей в дереве и хитро их кэширует, чтобы не перестраивались постоянно
+---
+--- Благодаря этому можно каждый раз создавать новые элементы в верстке, а получать старые :)
+function builder:build()
+    local root = self:_get(self.elementTree)
+    self:build_step(root)
+end
+
+function builder:layout()
+    self.elementTree:layout()
+end
+
+function builder:update(dt)
+    self.elementTree:update(dt)
+end
+
+function builder:draw()
+    self.elementTree:draw()
+end
+
+return new
diff --git a/lib/simple_ui/center.lua b/lib/simple_ui/center.lua
new file mode 100644
index 0000000..994c831
--- /dev/null
+++ b/lib/simple_ui/center.lua
@@ -0,0 +1,22 @@
+local Constraints = require "lib.simple_ui.constraints"
+local SingleChildElement = require "lib.simple_ui.single_child_element"
+
+--- @class Center : SingleChildElement
+local element = setmetatable({}, SingleChildElement)
+element.__index = element
+element.__type = "Center"
+
+function element:layout()
+    self.size = Vec3 { self.constraints.maxWidth, self.constraints.maxHeight }
+
+    if not self.child then return end
+    self.child.constraints = Constraints(self.constraints)
+    self.child:layout()
+
+    self.child.offset = Vec3 {
+        self.offset.x + (self.size.x - self.child.size.x) / 2,
+        self.offset.y + (self.size.y - self.child.size.y) / 2,
+    }
+end
+
+return element
diff --git a/lib/simple_ui/constraints.lua b/lib/simple_ui/constraints.lua
new file mode 100644
index 0000000..ab54dff
--- /dev/null
+++ b/lib/simple_ui/constraints.lua
@@ -0,0 +1,21 @@
+--- @class Constraints
+--- @field minWidth number
+--- @field maxWidth number
+--- @field minHeight number
+--- @field maxHeight number
+local constraints = {
+    minWidth = 0,
+    maxWidth = math.huge,
+    minHeight = 0,
+    maxHeight = math.huge
+}
+
+constraints.__index = constraints
+
+--- @param from {minWidth?: number, maxWidth?: number, minHeight?: number, maxHeight?: number}
+--- @return Constraints
+local function new(from)
+    return setmetatable(from, constraints)
+end
+
+return new
diff --git a/lib/simple_ui/element.lua b/lib/simple_ui/element.lua
index b2433c0..cc2099b 100644
--- a/lib/simple_ui/element.lua
+++ b/lib/simple_ui/element.lua
@@ -1,28 +1,40 @@
 local Rect = require "lib.simple_ui.rect"
+local Constraints = require "lib.simple_ui.constraints"
+local Vec3 = require "lib.utils.vec3"
 
 --- @class UIElement
---- @field bounds Rect Прямоугольник, в границах которого размещается элемент. Размеры и положение в *локальных* координатах
---- @field transform love.Transform Преобразование из локальных координат элемента (bounds) в экранные координаты
-local uiElement = {}
-uiElement.__index = uiElement
+--- @field type string
+--- @field key? any Must be convertible to string
+--- @field parent? UIElement
+--- @field constraints Constraints
+--- @field offset Vec3 Положение левого верхнего угла элемента в экранных координатах {x, y}. Устанавливается родительским элементом.
+--- @field size Vec3 Размеры элемента в экранных координатах {x, y}
+--- @field build? fun(self)
+local element = {}
+element.__index = element
+element.type = "Element"
+element.constraints = Constraints {}
+element.offset = Vec3 {}
+element.size = Vec3 {}
 
-function uiElement:update(dt) end
+--- "Constraints go down. Sizes go up. Parent sets position."
+---
+--- Karl Marx, probably.
+function element:layout() end
 
-function uiElement:draw() end
+function element:update(dt) end
 
-function uiElement:hitTest(screenX, screenY)
-    local lx, ly = self.transform:inverseTransformPoint(screenX, screenY)
-    return self.bounds:hasPoint(lx, ly)
-end
+function element:draw() end
 
 --- @generic T : UIElement
 --- @param values table
 --- @param self T
 --- @return T
-function uiElement.new(self, values)
+function element.new(self, values)
     values.bounds = values.bounds or Rect {}
     values.transform = values.transform or love.math.newTransform()
+    if values.child then values.child.parent = values end
     return setmetatable(values, self)
 end
 
-return uiElement
+return element
diff --git a/lib/simple_ui/flex.lua b/lib/simple_ui/flex.lua
new file mode 100644
index 0000000..1c072f3
--- /dev/null
+++ b/lib/simple_ui/flex.lua
@@ -0,0 +1,14 @@
+--- @class Flex : MultiChildElement
+--- @field direction "horizontal" | "vertical"
+local flex = setmetatable({}, require "lib.simple_ui.multi_child_element")
+flex.__index = flex
+flex.type = "Flex"
+flex.direction = "horizontal"
+
+function flex:layout()
+    for _, child in ipairs(self.children) do
+
+    end
+end
+
+return flex
diff --git a/lib/simple_ui/level/test.lua b/lib/simple_ui/level/test.lua
new file mode 100644
index 0000000..4dd5237
--- /dev/null
+++ b/lib/simple_ui/level/test.lua
@@ -0,0 +1,24 @@
+local ScreenArea = require "lib.simple_ui.screen_area"
+local Center = require "lib.simple_ui.center"
+local Placeholder = require "lib.simple_ui.placeholder"
+local Padding = require "lib.simple_ui.padding"
+
+
+return ScreenArea:new {
+    build = function(self)
+        return
+            (love.timer.getTime() / 2) % 2 < 1 and
+            Center:new {
+                child = Padding:new {
+                        left = 8,
+                        right = 8,
+                        top = 8,
+                        bottom = 8,
+                        child = Placeholder:new {
+                            key = "const :)",
+                        }
+                    }
+                    or nil
+            }
+    end
+}
diff --git a/lib/simple_ui/multi_child_element.lua b/lib/simple_ui/multi_child_element.lua
new file mode 100644
index 0000000..25ad1d9
--- /dev/null
+++ b/lib/simple_ui/multi_child_element.lua
@@ -0,0 +1,13 @@
+--- @class MultiChildElement : UIElement
+--- @field children UIElement[]
+local element = setmetatable({}, require "lib.simple_ui.element")
+element.__index = element
+element.children = {}
+
+function element:update(dt)
+    for _, child in ipairs(self.children) do
+        child:update(dt)
+    end
+end
+
+return element
diff --git a/lib/simple_ui/padding.lua b/lib/simple_ui/padding.lua
new file mode 100644
index 0000000..05c809e
--- /dev/null
+++ b/lib/simple_ui/padding.lua
@@ -0,0 +1,35 @@
+local Constraints = require "lib.simple_ui.constraints"
+local SingleChildElement = require "lib.simple_ui.single_child_element"
+
+--- @class Padding : SingleChildElement
+--- @field left number
+--- @field right number
+--- @field top number
+--- @field bottom number
+local element = setmetatable({}, SingleChildElement)
+element.__index = element
+element.type = "Placeholder"
+element.left = 0
+element.right = 0
+element.top = 0
+element.bottom = 0
+
+--- "When passing layout constraints to its child, padding shrinks the constraints by the given padding, causing the child to layout at a smaller size.
+--- Padding then sizes itself to its child's size, inflated by the padding, effectively creating empty space around the child."
+---
+--- as in https://api.flutter.dev/flutter/widgets/Padding-class.html
+function element:layout()
+    if not self.child then return end
+    local c = Constraints(self.constraints)
+    c.maxWidth = c.maxWidth - self.left - self.right
+    c.maxHeight = c.maxHeight - self.top - self.bottom
+    c.maxWidth = c.maxWidth > 0 and c.maxWidth or 0
+    c.maxHeight = c.maxHeight > 0 and c.maxHeight or 0
+    self.child.constraints = c
+
+    self.child:layout()
+    self.size = Vec3 { self.child.size.x + self.left + self.right, self.constraints.maxHeight + self.top + self.bottom }
+    self.child.offset = self.offset + Vec3 { self.left, self.top }
+end
+
+return element
diff --git a/lib/simple_ui/placeholder.lua b/lib/simple_ui/placeholder.lua
new file mode 100644
index 0000000..37cf069
--- /dev/null
+++ b/lib/simple_ui/placeholder.lua
@@ -0,0 +1,24 @@
+local Constraints = require "lib.simple_ui.constraints"
+local SingleChildElement = require "lib.simple_ui.single_child_element"
+
+--- @class Placeholder : SingleChildElement
+local element = setmetatable({}, SingleChildElement)
+element.__index = element
+element.type = "Placeholder"
+
+function element:layout()
+    self.size = Vec3 { self.constraints.maxWidth, self.constraints.maxHeight }
+
+    if not self.child then return end
+    self.child.constraints = Constraints(self.constraints)
+    self.child:layout()
+    self.child.offset = Vec3 {}
+end
+
+function element:draw()
+    love.graphics.rectangle("line", self.offset.x, self.offset.y, self.size.x, self.size.y)
+    love.graphics.line(self.offset.x, self.offset.y, self.offset.x + self.size.x, self.offset.y + self.size.y)
+    love.graphics.line(self.offset.x, self.offset.y + self.size.y, self.offset.x + self.size.x, self.offset.y)
+end
+
+return element
diff --git a/lib/simple_ui/screen_area.lua b/lib/simple_ui/screen_area.lua
new file mode 100644
index 0000000..f253f57
--- /dev/null
+++ b/lib/simple_ui/screen_area.lua
@@ -0,0 +1,28 @@
+local Constraints = require "lib.simple_ui.constraints"
+local SingleChildElement = require "lib.simple_ui.single_child_element"
+
+--- @class ScreenArea : SingleChildElement
+local element = setmetatable({}, SingleChildElement)
+element.__index = element
+element.type = "ScreenArea"
+
+function element:layout()
+    local screenW, screenH = love.graphics.getWidth(), love.graphics.getHeight()
+    self.constraints = Constraints {
+        maxWidth = screenW,
+        maxHeight = screenH
+    }
+    self.size = Vec3 { screenW, screenH }
+
+    if not self.child then return end
+    self.child.constraints = Constraints { -- force a child to be the same size as the screen
+        minWidth = screenW,
+        maxWidth = screenW,
+        minHeight = screenH,
+        maxHeight = screenH,
+    }
+    self.child:layout()
+    self.child.offset = Vec3 {}
+end
+
+return element
diff --git a/lib/simple_ui/single_child_element.lua b/lib/simple_ui/single_child_element.lua
new file mode 100644
index 0000000..45602f3
--- /dev/null
+++ b/lib/simple_ui/single_child_element.lua
@@ -0,0 +1,20 @@
+--- @class SingleChildElement : UIElement
+--- @field child? UIElement
+local element = setmetatable({}, require "lib.simple_ui.element")
+element.__index = element
+
+function element:layout()
+    if not self.child then return end
+    self.child.constraints = self.constraints
+    self.child:layout()
+end
+
+function element:update(dt)
+    if self.child then self.child:update(dt) end
+end
+
+function element:draw()
+    if self.child then self.child:draw() end
+end
+
+return element
diff --git a/lib/utils/vec3.lua b/lib/utils/vec3.lua
index ca9a10e..504ad39 100644
--- a/lib/utils/vec3.lua
+++ b/lib/utils/vec3.lua
@@ -78,8 +78,9 @@ function __Vec3:equalsTo(other)
         and self.z == other.z
 end
 
----Vec3 constructor
----@param vec number[]
+--- Vec3 constructor
+--- @param vec number[]
+--- @return Vec3
 function Vec3(vec)
     return setmetatable({
         x = vec[1] or 0,
diff --git a/main.lua b/main.lua
index 26825d5..a898089 100644
--- a/main.lua
+++ b/main.lua
@@ -2,7 +2,8 @@
 
 local character = require "lib/character/character"
 require "lib/tree"
-local testLayout = require "lib.simple_ui.level.layout"
+local UIBuilder = require("lib.simple_ui.builder")
+local testLayout = UIBuilder(require "lib.simple_ui.level.test")
 
 function love.conf(t)
     t.console = true
@@ -25,6 +26,8 @@ local lt = "0"
 function love.update(dt)
     local t1 = love.timer.getTime()
     Tree.controls:poll()
+    testLayout:build()
+    testLayout:layout()
     testLayout:update(dt) -- логика UI-слоя должна отработать раньше всех, потому что нужно перехватить жесты и не пустить их дальше
     Tree.panning:update(dt)
     Tree.level:update(dt)