I don't know anything about nottingham but here's what I have generically. Renting is probably cheaper than halls (but I guess it depends how expensive your halls are) but things to bear in mind are that you will probably rent for the full year rather than just the academic year. Bills may or may not be included, make sure if they are renting a room in an already shared flat (or if they use a buddy up service with a rental agent) that the others in the flat are also students as otherwise there will be council tax to pay (flats with all students in them are exempt). Some things might work out cheaper i.e. doing washing will be cheaper in the flat than in halls. Things that are probably included in your halls will be electricity and gas, internet access, contents insurance etc. You will want to establish what level of furnishing will be supplied e.g. appliances - they also might be more likely to require a tv licence in a flat. For example, it looks like rental for a 4 bed where DS is, is about £1k - £1.4k per month. So, say £250-350 per person per month, plus bills, maybe another £50 per month? His small, scruffy single bed non- ensuite room in halls is £113 per week for 40 weeks (Total £4520). His share of a flat rental looks like it will be about £3600 to £4800 for 12 months.
Usually I think it's 1 month rent up front as a deposit.
Take photographs of everything both on arrival and leaving. The landlord may require regular inspections, check how often these will be and whether they expect a tenant to be in or if not, are the agents retaining keys. Obviously also read meters if being liable for bills.
in terms of location, at DSs Uni, they are not in the city centre, and the accommodation is even further out. I think we'll maybe be looking at something between the city centre and the uni, try to keep near the bus route and check out the availability of a supermarket. Also consider if they need to be near sports facilities or work if they have a job. Upper floor flats are preferable (despite the stairs) as they are warmer and generally more secure.