if you have the cherry picker why not use it for most of the building 
Thats what i was gonna say
you will get better results
Wfp at that height is never as good as by hand plus hose is in a busy place etc
Is it a builders clean??? In which case wfp will be useless anyway and you will be in for some fun, they are hard work and very hard to price right... As a rule though i reckon you want to at least double whatever price you would come up with as a maintenance clean .... Are you doing it alone?
Sorry for all questions but they all make difference to the price.. If you are a sole trader id get some lads local to quote you a day rate and use that as you base, just make some money on top for overseeing it, and doing some yourself,
looks a nice job hope you get it