Even the elite had simple buildings, with a central fire and a hole in the roof to let the smoke escape; the largest homes rarely had more than one floor and one room. Buildings varied widely in size, most were square or rectangular, though some round houses have been found. Frequently these buildings have sunken floors, with a shallow pit over which a plank floor was suspended. The pit may have been used for storage, but more likely was filled with straw for insulation. A variation on the sunken floor design has been found in towns, where the "basement" may be as deep as 9 feet, suggesting a storage or work area below a suspended floor. Another common design was simple post framing, with heavy posts set directly into the ground, supporting the roof. The space between the posts was filled in with wattle and daub, or occasionally, planks. The floors were generally packed earth, though planks were sometimes used. Roofing materials varied, with thatch being the most common, though turf and even wooden shingles were also used.