Get in a high access equipment,
Scaffold towers are ok for bungalows, but would be a nightmare for houses, where possible keep off the roof!
Roof cleans (full) start at £750 for a bungalow and £1200 + vat for a house
We always do these as a 2 man team, when we had one pressure washer it would be about 8 hours start to finish with clean up.
The last bungalow we did with two pressure washers took under 3 hours
Darran