hi there
the big boys look for productivity rates anywhere from 2000sq ft per hour upwards, this will be on larger sites that have x number of operatives on them. they will more than likely have ride on a pedestrian machines covering floors, and therefore productivity rates can rapidly increase depending on the machine being used.
small companies usually work on prod rates of say 1300sq ft through to 1800sq ft per hour, the other factor that plays a part is that one operative on a site will clean at a dimishing prod rate if time on the site exceeds says 2 hours, therefore you need to consider that, instead of putting one operative on a site for 4 hours, split it 2 ops for 2 hours each.
costing work on a per sq ft basis, is a simple enough process, purely by allocating time to tasks, multiplied by area = times, x costs etc = rate charged.
regards
martin