Perhaps a little more info, ie is this just common areas or flats as well? is 12-16 hours 1 or 20 people?
what sort of cleaning will you be required to do? ie 200sm of empty space or 200sm of furniture, carpets contents clean etc etc.
this would be tough to guess for anyone who can help without the extra info
places can get real dirty in 12 months (however 1x12hours = £33ph seems a good rate to me)