How others are doing it is not my concern, I think the accepted way to do this is to get on a cat ladder, or even walk on the tiles and just pressure wash the roof. I will be working from a spider lift (apart from where this is not possible) and will be offering a professional service.
How I will be doing it will be to do a full roof survey, inside (where possible)and outside. The roof will then be pressure washed and the area tidied. This will include all gutterings and downspouts and any debris that has fallen. The client will then have different levels of further service, sealing, colouring etc, etc.
Sean - this will be a very sharp learning curve for me but I endeavour to offer the best service!!
Rob