Experimental house, "Roll It", is a collaborative project within Germany's University of Karlsruhe. The basic concept is as follows: using a cylindrical design to maximize space within a minimum housing unit. Not sure how "space efficient" this would actually be, but using it as transport could be fun (until the nausea inevitably sets in).
Via Arch Daily:
"Structurally, the prototype includes an outer shell with the four support rings over a rigid inner shell. A translucent membrane envelops the entire form and serves as advertising space for sponsors. Thin wooden slats are attached to the membrane to form the running surface of the roll.
The inner cover is a series of laminated OSB panels, each 15 mm thick, that cover the support rings. Circular openings in the side walls allow light into the structure, and a large opening serves as the entrance."