Exterior, House Building Type, and Metal Siding Material Perforated steel panels provide a contrasting sense of roughness and lightness, which Oman played with throughout the home's design. The skin adds transparency and graphic energy to the exterior, though Oman did worry about people fixating on the tic-tac-toe element. "It's like calling a rectangular building the Tetris house," he says.  Photo 2 of 10 in Super Minimal Steel and Concrete Villa with an Unusual Facade