I bought one of those Car wash poles from local garage. :

I use it for this purpose (and the car now and again)
Use washing-up liquid mix thicker than normal ( so quite soapy)
rinse wash rinse, simple!
When finished I clean the whole conservatory (Rinse roof with PURE water) wash conservatory with pole system as normal!

The last one I did took 4 hours I charged £115
The owner was prepared to pay more (I saw the wad of cash he just withdrew from his bank that morning to pay for the job!

)
So I think a minimum of £25 per hour in future...
Tell customer in advance Hourly Rate save embarrassment later!