How do I make a point and click?

Well, you see all the tycoons like Retail tycoon, and Azure Mines. I am wondering, how do I make a point and click system, where you can place down items like Retail tycoon.

Yes I am a scripter, the part that does not work for me is getting all the touching parts.

GetTouchingParts(PART) does not work.

First is it a model or a union your trying to place?