An estimated 100 million people around the world are homeless, a statistic that Alistair Parvin hopes to help change.In August 2011, Parvin helped start WikiHouse, an "open source construction set" designed to let those with little or no building experience construct sturdy, long-lasting homes. A would-be builder downloads free sketches of each piece of a house from the Wikihouse website, carts materials to a machine shop for carving, then assembles the house based on instructions, much like one would assemble an item of IKEA furniture."Two or three people working together can build a small house in about a day," Parvin said at a TED gathering Thursday, the Agence France-Presse reported.