Different types of roof have different slopes within the same building. Many traditional buildings incorporate different types of roof within a single composition. For example, a building with the primary mass under a hip may have a central projecting bay with a gable end and a front portico with a pediment. The type and shape of the roof on your home can help determine how well it will perform during a severe windstorm. Don't use the same pitch for each roof! Each type has its own characteristics and should have different slopes:
The gable roof is a very popular type of roof. The gable roof is easy to build, sheds water well, provides for ventilation, and is applicable to a variety of house shapes and designs. A gabled roof has two slopes that come together to form a ridge or a peak at the top, each end looks like the letter A. Homes with gabled roofs are more likely to suffer greater damage, such as collapse of the end wall from high winds because they are often not braced properly during construction.
The hip roof is slightly more difficult to build than a gable roof, but is still a popular choice. A hipped roof is one that slopes upward from all sides of the building. Because of its aerodynamic properties and construction techniques, most hipped roofs will perform better in windstorms than the second roof type: a gabled roof. It does not provide for ventilation as well as some other roof designs and increases the chance for leakage due to the hips and valleys.
The A-frame provides not only a roof but the walls as well. Originally, it was used for cottages, but in recent years has been applied to homes, churches, and other structures.
A flat roof is the most economical roof to build, but does not add much to the design of most houses. It requires a "built-up roof covering rather than conventional shingles. A built-up roof consists of layers of roofing, felt, tar topped with gravel. Actually, most so-called flat roofs are pitched 1/8 to 1/2 in per foot to aid in drainage. The flat roof is popular in warmer areas of the country where wide overhangs are desirable for shade and where little or no snow falls.