Roof replacement on flat roof is often a matter of practicality more than a matter of style. That is, commercial building owners' main concern when installing a roofing product, is choosing something that is going to be durable and no-nonsense. They don't care as much about having something that is particularly stylish. Flat roofs need to be more water resistant because they have to deal with standing water. Also, since they are often not visible from the ground, some building owners don't care at all what they look like.