ONCE UPON a time in America, when a farmer needed to build a barn, the local community would come together for a combination of work and celebration as folks erected the frame and raised the roof. Now British-based architect Alastair Parvin has taken that concept into the 21st century, looking to pull together the global community to design and produce homes. The concept is relatively simple. Visitors to WikiHouse.cc can share design and construction specifics. As these develop into coherent, buildable projects, they are posted on an open library. The plans are more than just plans; they are downloadable files that can be fed into a CNC (computer numerical control) machine capable of cutting wood or other materials to exact specifications. It kicks out the components. “The parts are all numbered and basically what you end up with is a really big IKEA kit,” as Parvin put it in a recent TED Talk. Several simple prototypes have been assembled. The idea is so fresh that no livable house has actually been built yet, but don’t be surprised if someday soon a friend invites you over to raise the roof.