No, I would never advise or send anyone onto a 2 story level roof. I was talking about a kitchenette type roof that would be sloped to accomodate drainage. And you never work from the ladder, that is purely for access and egress. For a 2 story roof you would need a cherry picker articulated boom MEWP, the one in the foto supplied by the other chap is your only man for what you need. If its not in the budget don't even contemplate getting up on that roof. Wet moss is a killer. Your insurance won't cover you either. Don't put the cradle of the boom through the roof either, if your not confident, the newer machines are very sensitive. You will need to get very close to scrubb that moss off those slates if they have not been done in a while. I don't think you'll get the agitation telescopically, into the ridges and all. You cant just use a pressure washer or you'll get a zebra effect when it dries. Nightmare job if its your first, I'd pass. Don't let the water go up under the lead flashing or your in bother. Its a no brainer but some guys wouldn't know.