We would spray the roof, rinse the whole thing and then probably Bleach wash & rinse the valley's with the painted metal. Depending on how warm the temps are, I might section off the roof and do the process in pieces, so the paint does not start to come off.

Also, what color are the shingles & how infested is the roof?? Reason I ask, is that we clean most roofs with a 2.5% or 3% solution. Whihte three tabs and really nasty, mossy roofs is all we use a 4% for.