The roof is either EPDM or TPO. The easiest way to determine which you have is to remove the vent shroud from the bathroom vent. The roofing material was cut and folded/stapled to the rafters so the vent could be installed. If the roofing material is white on top and black/charcoal gray on the bottom, it is EPDM. If the material is white on top and bottom, it is TPO.
Essentially both can be cleaned with Blue Dawn, warm water and a medium bristly brush. I use a hand brush with nylon bristles similar to the kind used to clean chrome wheels on a car. DON'T use a wire brush or a stiff bristle brush.
You can find information on care and maintenance of both types of roofing at:
http://www.dicorproducts.com/resources/rudys/
Download "RUDY'S EXPERT ROOF CARE HANDBOOK" at that website.
Good Luck