In housing design, the overall form (or "massing," as it is called in arch biz) is largely an interaction between plan and roof. Roof forms carry with them powerful symbolism and can help create order out of a complex plan. Theoretically, the simplest roof is flat. Many styles—including today's "post-modern" designs, which often suppress the roof by using the facade as the chief organizing element in the design—depend heavily on them. Frank Lloyd Wright used flat roofs, or roofs with very low pitch (slope), so that only the roof edge and overhang counted in the design. Flat roofs can work with any house plan, which helps to explain how Wright developed such ingenious and perfect