Building System

Basically I made a building system and it works fine. however when ever for every time I build the block gets higher and higher.

Code:
local RunService = game:GetService(“RunService”)

local ContextActionService = game:GetService(“ContextActionService”)
local UserInputService = game:GetService(“UserInputService”)
local LeftClick = Enum.UserInputType.MouseButton1
local Wood = script.Parent

local camera = workspace.CurrentCamera

Wood.MouseButton1Down:Connect(function()

SelectionBox = Instance.new(“Part”)
SelectionBox.Parent = game.Workspace
SelectionBox.Name = (“SelectionBox”)
SelectionBox.Size = Vector3.new(18, 3, 3)
SelectionBox.Material = (“Neon”)
SelectionBox.Transparency = 0.7
SelectionBox.Color = Color3.fromRGB(0, 255, 0)
SelectionBox.Anchored = true
SelectionBox.CanCollide = false

local RANGE = 1000
local RaycastParams = RaycastParams.new()
RaycastParams.FilterDescendantsInstances = {SelectionBox}
RaycastParams.FilterType = Enum.RaycastFilterType.Exclude

local function render()
local mouse2DPosition: Vector2 = UserInputService:GetMouseLocation()
local mouse3DRay: Ray = camera:ViewportPointToRay(mouse2DPosition.X, mouse2DPosition.Y, 1)
local raycastResult: RaycastResult = workspace:Raycast(mouse3DRay.Origin, mouse3DRay.Direction*RANGE, RaycastParams)
local mouse3DPosition

if raycastResult then
	mouse3DPosition = raycastResult.Position + Vector3.new(0, SelectionBox.Size.Y*0.5, 0)
else
	mouse3DPosition = (mouse3DRay.Origin + mouse3DRay.Direction*RANGE) + Vector3.new(0, SelectionBox.Size.Y*0.5, 0)
end
SelectionBox.Position = mouse3DPosition

end

local function Placement()
local Wood = Instance.new(“Part”)
Wood.Name = (“Wood”)
Wood.Parent = workspace
Wood.Color = Color3.fromRGB(106, 57, 9)
Wood.Material = (“Wood”)
Wood.Size = Vector3.new(18,3,3)
Wood.Anchored = true
Wood.Position = SelectionBox.Position
Wood.CanCollide = true
ContextActionService:UnbindAction(“Placement”, Placement, false, LeftClick)
SelectionBox:Destroy()
end
RunService.RenderStepped:Connect(render)
ContextActionService:BindAction(“Placement”, Placement, false, LeftClick)
end)

Video:

External Media