The Hexayurt Project looks great, tons of info and more on the site…
The Hexayurt is a prize-winning shelter you can build yourself for about $200 (backup link). Suitable raw materials include common building materials ( fire safe insulation boards,) hexacomb cardboard and plastic. You cut six 4′ x 8′ panels in half diagonally to make the roof, and use six more whole panels to form the walls. It takes about two hours. The design (backup link) is in the public domain.
Different materials are appropriate for different uses – insulation, extended life, low cost, durability in extreme environments and so on. The design is in the public domain, and is in active development as a Free/Open Source style project.
The Hexayurt Project also includes groundbreaking work (pdf) (backup link) on providing simple services like interior lighting at incredibly low cost.