a lot of folks suggest a detergent, such as spic n span.
I've used that
and I have used laundry detergent too.
My last time was with barkeepers friend. I was up there scrubbing the oxidation from my nose cap, and when i was done.... and since I was up there with a rag and a hose, i just kept going...
I think it depend on what the dirt is that's up there.
and what you roof material is.
The biggest concern is staying away from mineral spirits and solvents with the EPDM and TPO membranes