In Washington, rain is a pretty common occurrence, so it’s vital that you have functioning drainage systems. Soft or impacted spots on a roof are very good at collecting water—especially on flat roofs—so making sure your roof is structurally solid is extremely important.
This includes both the structure and pitch of the roof, as well as its gutters. Water can be extremely destructive if not diverted and controlled properly, resulting in potential soil erosion, structural damage, mildew, mold, etc.
Functioning gutter systems are also crucial. Gutters direct water away from a roof to mitigate/avoid soil erosion or structural damage. If gutters are clogged or damaged, they will not be effective drainage tools. The most standard type of gutter you normally see installed on a house are K-style gutters, which are usually made out of aluminum.