I clean loads of these, in fact done 1 today!!
You be surprised how easy the green slime comes off. I have a pole dedicated to cons roofs which i connect to a hose which is connected to...........an outside tap and thats all i use......water!!!
If you have tree sap on the roof then you can use a non-caustic TFR. I advertise this service heavily, and get real busy doing it, i love it, so....water a brush and elbow grease......todays roof took me 30 mins, not been done for 6 yrs!!