Hi Rob,
If it is you and a partner/ friend doing the work. Price on what you want to receive each day for working (£250 - £350 each); you will also need to build into the cost the cherry picker if this is hired. If it isn’t hired and you own it, charge £30 an hour for that. If it is your staff carrying out the work, charge their wages plus your normal profit margin. Also, add in 5% on top of the total price, to include blades, squeegee blades etc.
This is only a guide and everyone may price different, I would not be able to give you a definite price without looking at the job and seeing what is involved.
Also make sure you have a site visit and check all the windows first, incase any are scratched/ damaged, if you find them, point them out to the site manager, make a note of them and get him to sign a waver, stipulating you are not responsible for these windows. In addition, if they look fine and then when you start cleaning them, you find they are damaged in anyway. Stop work immediately and point these out to the site manager. Clean several in-front of him, so he can see the damage is already there and it is not down to your cleaning.
Hope this helps
Andrew