thanks very much people
Daz, yeah thats what i thought about self cleaning conny roofs & windows i wouldnt trust the stiff vikan not to damage the coating layer!
Ive just put the stiff vikan on my 35 ft unger glass fiber pole tested for leaks and good to go!

Gonna use fairy or evans hard suface cleaner at a strong mix in my bucket. then using t-bar applicator and trad pole wet the plastic corigated conny roof up good.
Then leave to soak (if the suns not out, drying it too qucikly that is!) then use custys outdoor water tap connected to my w.f.p and blast it at a reasonbly high preasure but not too high as to damage the roof of course.

and scrub it
then finally wash down using pure water for a clear steakless finish!

I'll do some before and after pics too to show you all how it went!
hows that sound to you all?
any suggestions very welcome!
regards, GB