Cleaning the roof

My parcel yesterday is in the extra. It is a telescopic window cleaner mop. There are so many patches of black mould on the glass and I need to clean them. I gave it a first clean this morning and it's not done  too badly. The rain will rinse off the soap. I do need to climb the ladder and scrub the worst patches and clean the inside. I'm going to do it in stages, the window cleaner was a great new asset. 
Thank you for all your great guesses yesterday I would love a metal detector, perhaps I'll start saving!