Most common black stains on your roof are most likely black mold….if there is a green furry patch that is most likely moss. This can all be treated with soaps and detergents. Please do not scrap this off or power wash it, this can cause major long-term damage. There is proper ways of removing these molds and it has to be done by a professional. If you called a company and they said it needs to be power washed please run the other way. Here at power wash unlimited we have many years of experience in cleaning these types of mold and its all done with soaps and detergents give us a call and we can assist you in getting your roof back looking great.