You will need a second person (water boy) dont forget floor ares of schools are enormous, you dont want to be walking to the cleaners cupboard there and back with clean water, dirty water time and time again etc etc, plugs arent allways where you want them, a second person is invaluable, they will do things like that for you.
I allways price it that the rooms have been pre vacced by the cleaners and chairs are up, if chairs are down its X% more. That way the rooms will be prepped for you. School I do the caretaker puts all the chairs on the vinyl round the sink so its a clear room and its reflected in the price.
Good Luck
Murky