I don't think anybody can answer this queston. There is no size or even type of facility. Big difference for 100 offices, 100 hotel rooms or a warehouse occupying the same square footage.
One guy does a 400 x 400 sqft building. But guess what, he only does the offices which are mostly on the perimeter, the break room, rest rroms and the hallways. The rest of the building, he might dry mop the floors.