People have always needed to shelter from the weather, and somewhere warm and comfortable to sleep at night. The design of most homes throughout the world depends on the climate. People living in hot countries need their homes to be cool and airy as possible, while people in cold countries need their homes to be snug and warm. The materials that people use to build their homes usually depend on what they can find around them. Stone, mud, straw and wood are all natural materials that have been used to build homes for thousand of years. By contrast, many modern homes are built from artificial materials such as concrete, steel and glass.