Okay, the spreadsheet we used at Milvia is here. The spreadsheet adjusts each room's rent according to:

• Square footage
• Share of the common space (this increases if the room has multiple occupants)
• The proportion of rent dedicated to paying for common space
• Arbitrary adjustments to specific rooms' rents (e.g. to reward the person doing the work of collecting rent & utilities, or to allow bidding on rooms by figuring out who is willing to pay the highest positive adjustment on a particular room)