I share warehouse space with a handyman contractor who cleans roofs. I think he use high flow lower pressure . Sounds like a real pain in the ass because the people who are willing to shell out the money to clean a roof usualy have nice landscaping , windows, decks, etc , that need to be covered in plastic before the chemicals and slop gets washed off the roof. He has did ok with it but I think unless you live ina major metro area or in a h.o.a. neighborhood that requires you to keep your house clean I don't see much of a market for it