professional roof cleaners do not use pressure washing to clean roofs.
the best way is to scrape the moss off the roof first. this can be done with extendable poles and special attachments that fit the roof tile. With the attachment reversed the wire brushes then completes approximate;y 80% removal of moss from the roof. A mobile scaffold tower can be used to access the roof and a roof tile need never be stepped on.
A low pressure biocide cleaner is then applied and agitated into the tiles. You get an immediate result and the chemical continues to work safely to prevent regrowth of algae, litchen and moss for approximately 5 years.
If you want anything to last 'professional' maintenance is key. I don't think a roof that protects your most valuable asset is any different. Statistics also show that buyers form an impression of your home before they've even entered. Yes a clean roof can really help sell your home!