This is the kind of job that I would generally try to avoid, particularly if they want a full external clean, you will never get a good enough price to make it a good earner.
With commercial work I love the stuff I can charge between about £35 up to about a £150 or so.
That may not sound like large sums of money, but the time taken to do the work makes these accounts the absolute cream of my round.
Large commercial accounts where a fair price might be in the several hundreds of pounds, usually means they will be looking very closely at what they are paying out, often with the large national companies pricing for them, meaning prices will be incredibly tight and the operatives doing the work will be doing the barest minimum amount of work they can get away with.
I have one account, a - Wetherspoon's - They have the pub windows cleaned inside and out every week, the lodge windows are on request and I then do it in bite sized chunks over a period of weeks.
I can charge an extra £20 to £40 for the work done, this means it's small enough that they are not too concerned about it being added on to my normal bill.
This of course is nothing like as large as that hotel mind! But it is worth £220 per month for the weekly stuff.
So as Alex has said, try to get them to have the high usage areas done regularly, thereby allowing you to give what seems a reasonable quote and adapt a more variable system for bedroom windows and the like.
Oh, and make your payment terms very, very clear!!!!
These places can leave you waiting months for payment if they can get away with it!
Best of luck with your quote!
Ian