How do i make a build tool?

Yes, i'm trying to make a building game, it gives you 1 place, on a baseplate, BUT, i need help on how to stop players from greifing other plots AND making your own build tool that you can switch between Colors, and materials, and shapes, can you help?

i cant even figure out one thing of code, help please

Here is a briefing. This might clear up some confusion and give you a place to start:

--[[

1)  Make the gui
2)  Connect buttons to functions
3)  Disconnect events when necessary
4)  When a build button is clicked, use game.InsertService:LoadAsset(########) to insert a model
5)  Connect mouse events
6)  Use :MoveTo() to move the model to the cursor position, not allowing it to move to areas outside the base
7)  Add a integer value called "OwnedBy" to the model, and set it to the userid
8)  Disconnect mouse events on click/exit
9)  Edit tools must make sure the OwnedBy value == the current user's id
10)  Clean up the code a bit for efficiency

]]