I'm looking for advice on how to clean an 86 year old cement asbestos tile roof. The roof appears to be structurally sound, however it's rather unsightly as it's coated with dirt, mold, moss, etc. Also, the very top of the roof is flat, possibly coated with copper, and it has "bled" down onto some of the shingles turning them red and rusty. Any help or advice will be greatly appreciated.
I have thought of everything from power washing the shingles with a chemical wash to using bleach and a brush, but I'm just not certain as to what I should or should not do (and I've received conflicting opinions from different people).