Traditional roofs are nearly always pitched (sloping) at angles of 26.5 degrees or more. Roof slopes were set out using simple proportions of height to span. For example, a 26.5 degrees slope is also known as quarter-pitch, the span being four times the height of the roof.
The sloping surfaces of a roof direct rainwater to the ground, usually first collecting it in gutters which convey the water to downpipes and thence away from the building. Some early buildings never had gutters, and require special care to paving and site drainage to keep water out of the building.