Moisture from above . Roof leaks are not limited to a certain kind of roof. Many folks are convinced that a shingle cover over their flat roof will cure all of their problems. Generally, shingle roofs do offer less maintenance than flat roofs, but they too can have problems, particularly if they are not installed properly. The best insurance against roof leaks is to hire a quality contractor to install your roof.
Warranties are nice if the contractor can fix the problem.
A quality contractor should install the right materials in the right manner, which will reduce the chances of developing a leak later on. You might spot an obvious problem. If you don't see a problem, get out a hose and water down the roof. Run the water down from the high point of the roof so the water travels over the area of the leak. Observe the water flow carefully, looking in areas that might look vulnerable to leaks.