The "Tiny House" movement is definitely gaining ground among the eco-friendly communities. By building on a trailer chassis, you are exempt from most local zoning laws, especially the ones governing minimum square footage. Most are built on the site they will occupy, or are moved once to their final location. Many are set up for "off the grid" living, with solar power, LED lighting, propane, and wood stoves for heating. Not my cup of tea, but there are definitely some fun and interesting designs floating around the internet for purchase.