No matter how good of a quality you have used as your roofing material, it won’t work well if you don’t have proper drainage services. At the end of every roof, you will find a gutter, running down towards the ground. The primary purpose of this gutter is to help rainwater flow down from the roof towards the ground and not causing water accumulation.
Original Source: https://modernsealroofing.weebly.com/blog/some-roof-drainage-considerations