Vince,
a conservatory ladder is held off the guttering by a glazing suction pad which is attached to the centre of the ladder.
This suction pad attaches to the glazing and acts as a stand off and a stability device.
At the top of this section of ladder is a hinged second section which has two horizontal spreader bars which sit on the underside of ladder section.
This hinged section is lowered onto the roof struts and disributes the weight evenly and safely. It also has a kneeling platform on castors running up and down the ladder, which allows the cleaner to move up and down the area of the roof in safety and comfort.
What I have found is that once you are up there, a roof is actually a very small area to clean!! and pretty easy too
I tried traffic film remover yesterday and was not impressed.
I have upvc cream cleaner which I apply on a wet sponge then hose off with tap water and giving it a final wash and rinse with pure water.