AutoCAD is used for drafting. It's not free but it shouldn't be hard to find if you don't mind illegal downloading.
Just look for AutoCAD on bittorrent. Although it would be a lot better to just buy the program. A lot of professional architects use it for their work. I'm using it for 3d and interior design. Really a cool program, but you need to have algebric knowledge to use it.
Google Sketch-Up is the one to go with.

But you need a good computer so that it wouldn't lag like hell when you use it.
Quote by RoamingConflict
This one dream involved me, one random girl, midgets and a pie.

...and midgets ended up f*cking her. I got the pie.