Roofs are fundamental to all shelters. They protect the inhabitants of a building from rain, snow, wind, sun, and heat or freezing. Types of roof, and the materials used to cover them, have varied over the centuries, changing with geography, innovation, and technology. A wide range of roofs exists around the world even today.

Primitive huts probably had roofs made of straw rushes, reeds, palm leaves, or a similar material, depending on what grew locally. Such "thatched roofs" had to be constructed at a steep angle, to allow rainwater to run off. Later mud was mixed with these materials, to provide strength, and eventually the reeds and rushes were replaced with branches from trees and larger timbers. Mud, clay, or other materials could then be used to create a mostly watertight roof.

In areas with little rainfall, such as the Middle East and the American southwest...