Hi Bill,
Like you I have done a few, but to be honest I am not 100% sure on the pricing. I only seem to do them for exisitng domestic customers, as an extra job.
I use my jet wash, as I purchased some extension for the lance, and I have an extendable pole with a brush on the end that attaches to a hose, which from memory I paid 20 quid for. I also have one of those platform ladders.
pricing obviously depends on the size of the conservatory but usually in the range of 20-30 quid, and takes me a couple of hours. If it is any help, my window cleaner charges me £10 to do the windows and door of my conservatory, and will not touch the roof.
Hope this helps
Paul