
I took a peek at some drawings on the Tiny House Forum (definitely worth trolling for examples and info,) which were made with a program called floorplanner. Here's one I made playing around with the program, which is super easy to use.It's also free to sign up. With the free account, you can work on/ edit one project. It's worth playing around with, and is helping me get some context of what fits in a tiny space.
Everyone should try it out:) It has a sexy 3d render function, so you can see what the house would look like. Very cool.
Update: Google sketchup is also a good option for drawing and rendering in 3d, as far as free software is concerned. This is a pretty sweet image drawn in it, from the Tiny House Forum.