Item / Building Placement (?)

What I think would be useful would be the Mouse object.

It has a few things that would help you:

• Player:GetMouse() (returns a Mouse object)
• Mouse.Move (event that fires when the player moves their mouse)
• Mouse.Hit (CFrame property that is the point that the player's mouse is 'touching')
• Mouse.Target (BasePart property that is the part the mouse is 'touching')
• Mouse.TargetFilter (Instance property where the instance and it descendants get ignored by the Hit and Target properties)

You can easily move a part with these, for example:

-- LocalScript
loca Player = game.Players.LocalPlayer
local Mouse = Player:GetMouse()
local Part = game.Workspace.ExamplePart

Mouse.Move:connect(function()
	local Position = Mouse.Hit.p
	Part.CFrame = CFrame.new(Position)
end)

Hope I helped!

~TDP