Corrugated metal roofing is basically a choppy metal sheet used commonly for barns and industrial buildings. Each sheet has a wave like pattern similar to that you see in a corrugated cardboard. While some consider it a functional eyesore, if you see what it can do, you won't feel bad about having this installed.
The price of it is much cheaper in terms of price and lighter in weight when compared to a double layer of ordinary metal roofing because you get the same strength without any additional expense.