Why are some roofs flat and others at angles? Builders choose roof styles based on the local climate, the cost of the roof, and the purpose of the building. Roofs with acute angles at the top have very steep slopes.
Why It Matters
Most roofs are either flat or have some sort of a peak on them. However, well-built flat roofs aren't actually built on a straight angle. They usually have a very obtuse angle—almost 180 degrees, but not quite. This makes it easier for water to run off the roof in the rain. A truly flat roof is fine in a desert climate, but it would quickly develop leaks in a rainy climate.
People who live in areas with a lot of snow or rain often build houses with acute angles at the top. These steep roofs allow snow, ice, and rain to slide off, and they're unlikely to develop leaks. However, they are difficult and expensive to build. They also make the house feel warmer in the summer, so they're not appropriate for hot climates. If a builder uses the wrong roof angle for his climate, disaster may result.
See for yourself: http://www.youtube.com/watch?v=415n0dbcuQM
Read the article at the following link, and then answer the questions below.
Why is a flat roof popular in a desert climate? Why do people in wet climates prefer steeper roofs?