Rental units that are vacant and available to be rented now communicate their relative size (along with the price and how frequent you'll have to pay) when you 'check' a door.
The sizes are communicating that the unit has:
A Small unit will have less than 3 rooms,
A Medium unit will have more than 2 rooms and less than 6 rooms
A Large unit will have more than 5 rooms.
Please note that this is not a measure of quality. Quality is generally reflected according to where in the city the rental is.
