This is a very cool idea... I think i'm going to make this thing out of card and fill it with great stuff and cardboard, then plaster or spackle the outside to make the curved parts...
I hear it's not that strong structurally. Has anyone though of just reinforcing the inside with some cardboard braces? You could use newspaper board too. It's really strong stuff. I made some armour from cardboard once that was strong enough to take a bullet (from a BB gun

). I mean, you can't make a house out of just walls and roofing... you need rafters, structure.
Just a thought.