In his short story “–And He Built a Crooked House” the great Robert Heinlein had a character cautiously opine that a house is, by and large, a device to keep off the rain. This is quite accurate. If you are wet, or your stuff, then life is not good.
And so all house design is tied closely to climate, and the materials available. Steeply sloped roofs speak of shedding snow. Flat roofs are for desert climes. Stone houses with stone roofs are built in stony regions, while earthen walls and sod roofs are for stone-free and timber-light conditions.
At this moment I am in Washington state. They’re having record rainfall. This is a good thing, since without plenteous rain there are wildfires in summer. People spend their home maintenance dollar coping with the rain. A good tight roof is a prerequisite, and if it’s fireproof metal then so much the better.
But then you get this kind of thing. This is a service building in a park, not a structure that gets a lot of love. It has a wooden roof, probably cedar shake. Because of the copious rain this roof may not actually be that old. But it’s got a couple seasons of growth on it, to get that deep cushiony moss and the rampant ferns.
Moss is a major problem for structures in this area, and there’s a considerable industry devoted to washing it off of manmade structures. The older residents of the region have mostly adapted to it, however. These trees for instance have formed a symbiosis with the moss!