Just be careful not to put down that you like listening to heavy music till 4am in the hope that you won't have to share, or they may very well pair you up with someone who really does do that each night.
Its an unfortunate fact of any university that some people do not make it through till the end of the first term, and whilst durham's drop out rate is one of the lowest in the country, it does still happen.
This means that they can re-allocate rooms if they need to within a couple of weeks, so if there are any problems with your roomate just go and speak to someone and it will be sorted. The "someone" you would need to speak to can vary from college to college, but your JCR/SRC exec will know who it is, and can point you in the right direction.