I have never made a bid for this many building but I think I would bid per foot. Do about a hour test for them for free and show them what you can do and find out how much you can do per hour. By the number of doors there is about 6000 feet plus the gables at 10 feet high. If you can do 80feet of an hour, .75 per foot would give you about $60 an hour.
Sounds like a good job to be doing when the weather starts to cool off. You will not have the water flying so high