Guess how long it will take you to do a drop. A drop is defined as one section from where you go over the edge to where you get out of the chair. Let's say it's an hour. Now count up how many drops there are and you will have the number of hours it will take you to clean that building. Let's say it's fifty hours and you charge $50 an hour. Submit the bid at $2,500.00. Now if you don't know how long a drop takes don't bid on buildings like this until you do. Go watch it being cleaned by the company that gets the bid or watch videos on not only how to do a building like that but pay close attention to long it takes per drop if you don't know how long a drop takes.
It can be quite dangerous, I think it's better to leave it to the professionals. At work we hired professionals from commersial window cleaning service here in Auckland to clean the windows on high-rise skyscrapers. These guy did all work at the highest level.