I have a placement system that snaps to a grid, how would I go about adding a function that detects whether the area already has an object in it? I'm not asking for a full code but links, snippets of code and explanations would be useful.
Try using Region3 or the FindPartsInRegion3 function : http://wiki.roblox.com/index.php?title=API:Class/Workspace/FindPartsInRegion3