Well i can give you a few ideas, If you want a good chemical mixture for your algea and mold contact owen-cornings they are a roofing (shingle)manufacture, I had the mixture a while back but dont have it now. It will remove all of it. Far as the roof use a pitch witch the spayer is on wheels rolls up and down the roof, You can apply your mixture thru downstream and then rinse low pressure,using the pitch witch. I made my own years ago they are very easy to make. I was a journyman roofer for over 18 years, before i got into this business and i cant stress enough If its not a walkable roof stay off, the risk for slipping by yourself or workers even damgage to the roof is great. Also make sure your insurance covers any roof work you might be doing,If they dont know your doing that type of work they might not cover a claim, Hope this helps... Tom |