I'm in halls at Liverpool at the moment...I'm on the Greenbank site in Roscoe and Gladstone hall.
I have to say that there is a much higher demand for self-catered rooms than there are self-catered rooms! there are some on campus (mulberry court etc), but if you want a lively atmosphere (which it sounds like you definately do) you HAVE to choose either Greenbank or Carnatic, which are full of 1st year students. You meet so many more people here so dont be put off if the rooms look a bit shabby. You'll be lukcy to get self catered but dont be tempted into private accom. A friend of mine did and is stuck with 5 2nd years that all knew each other before! It's worth putting up with a bit of a shabby room for the friends and atmosphere you get a halls on Greenbank/carnatic.
The rooms in Roscoe and Gladstone are alright...you share a bathroom with 6 people which sounds gross but its really not that bad, i've never had to wait for a shower and it gets cleaned for you every day! the rooms are fairly modern and decent sized (bigger in general than rooms at carnatic). In Derby and Rathbone there's a real variety of rooms. Some of the catered rooms have big kitchens you can chill in but others (the old court) are quite dated and basic but the rooms are MASSIVE! You'll be lucky if you get an en-suite cos everyone wants one, so dont hold out for one.
I know what you mean with the no room to hang out in, it was a bit annoying at first...but you can chill in each others rooms and its realllly not a problem, especailly when you form your close friendship groups and you can slob out and watch tv. They do have TV rooms and things that you can use if you want to, but most people just hang out in each others rooms. Even though it's not ideal it's awesome if youre off out and everyone on the corridor props their doors open-makes it really sociable and friendly!
AND if you're catered eating tea and breakfast together is realllly sociable and a great way to meet people is in the queue for tea
My advice would definately be go for Carnatic or Greenbank...the rooms really are FINE. If you're lucky (and your applying early so youre in a good position) you might get the self catered that you want but even if you dont, don't stress...the food is alright and it's worth putting up with for the craic!
Hope this helps, lemme know if you want any more info!!!