Yurts, another housing option I was looking at. Very compact (but can be expanded), super cheap, and really fast to build (we're talking ONE WEEKEND for the simpler ones). Can be hooked up with power and plumbing, you can add interior walls, lofts, decks, you can connect several together if you need more space.
SMILING WOODS YURTS This company creates customized yurt house kits. I think I really need to build my own unique house. The website says they help make your building experience as enjoyable as possible and use recycled materials and environmentally friendly products and materials whenever possible. Now to find a home site!
My wife, daughter and I lived in a yurt while building our off-grid house in Sandpoint, ID. We found it very difficult to leave it's "roundness" when we moved into the main house. We still use it as our retreat.