When a Missouri man with the destruction of Joplin on his mind began formulating how he'd like to build a home, concrete became the key building material. The 2,400-square-foot, three-story home (with a walk-on roof) is squarish-looking, with exposed concrete walls, both exterior and interior. The home is designed to be tornado-resistant. The walls are built with pre-stressed concrete, reinforced with rebar and 16 pre-stressed high tensile steel cables pulled with a hydraulic jack to thousands of pounds of pressure and permanently bonded with the concrete, according to www.rockspan.com, a Web site where the owner posts information about the house.