Looks like a fun clean
Ones arms and shoulders may well be aching by the time you have done that one
(providing you get the job of course!)
Hard to tell how high it is from the picture.
Do they want method statments and risk assesments etc?
As for pricing, imagine you are doing it off a ladder. I know it doesn't look like an account you could do off a ladder, but that should enable you to cost it out.
What about frequency?
If they are only going to want it done 3 or 4 times a year, it'll be a hard clean every time.
If it was being done off a cherry picker of some description then you are going to be cheaper at least by the cost of the days hire of one of them.
Best of luck, make sure you let us all know how you got on with it, whether or not you got it, and if you did, how you went about cleaning it.
Ian
