Are you sure it’s moss? Mosses are fairly thick plants that prevent water from flowing normally and promote infiltration. The green-to-grey colouring of the tiles can be explained more often by the presence of algae or lichens. The proliferation of these undesirable substances depends on climate, prevailing winds and even pollution in the air. Little compact snow can detach them naturally. Another solution, less random is annual maintenance which consists of spraying a suitable product, the least toxic possible.
Your roof gutters leak? Unless they are your gutters and you tell yourself it’s not a big deal? Big mistake, neglecting these small leaks could cost you. What impact for your home? Attention danger.