Client script for a Roblox build mode system

BuildClient.lua

local UserInputService = game:GetService("UserInputService")
local RunService = game:GetService("RunService")
local Players = game:GetService("Players")
local Building = false
local Mouse = Players.LocalPlayer:GetMouse()

local Brick = script.Part

local function RoundVector3(vector: Vector3)
	return Vector3.new(
		math.floor(vector.X),
		math.floor(vector.Y),
		math.floor(vector.Z)
	)
end

UserInputService.InputBegan:Connect(function(key, gp)
	if gp then return end
	
	if key.KeyCode == Enum.KeyCode.B then
		Building = not Building
		if Building then
			Brick.Parent = workspace.Building
			return
		end
		Brick.Parent = script
		return
	end
end)

RunService.RenderStepped:Connect(function()
	if not Building then return end
	
	local target = Mouse.Target
	if not target then return end
	
	local position = RoundVector3(Mouse.Hit.Position)
	
	Brick.Transparency = .5
	Brick.Position = RoundVector3(position)
	print(position)
end)

Mouse.Button1Down:Connect(function()
	if not Building then return end
	
	local target = Mouse.Target
	if not target then return end
	
	local clone = Brick:Clone()
	clone.Parent = workspace
	clone.Transparency = 0
	
end)