I did one about 2 years ago.
I washed it first with wfp.
Then opened it up and washed it wfp purewater, no detergents
Then got on the steps and ladders and used cloths.
Theres a lot of nooks and crannies that would take forever with a brush,also theres a bit of oil grease on the metal frame joints.
Took longer than expected as usual,but they were delighted with it.
I think I charged £120.
They weren't regular custies or I might have charged less.
They later got me back to do full conservatory and windows.
P.S Dont do it when its windy,this one had a sensor on it that made it auto close when it felt a gust.