Hi Craig
I take it your not wfp??
This would be the easiest method.
Before i used wfp i used to use a soft broom, detergent and a hose pipe aslong as the customer had and didn't mind you using the outside tap.
I then used a squeegie on an extending pole.
I find that pure water cleans the con roof just fine, but you could always use TFR (Traffic Film Remover) if your not wfp.
Craig