I got a form and I had to number *all* the choices in preference order(they had the cost next to each too), so was a bit worried as I didn't want my 6th choice so much.
I'm going to be in Refounders House so got what I wanted: self-catered, single, non-ensuite room. Sharing kitchen/lounge and bathroom(s) with 6-10 people, I think we will have a front door so it's like a house share but with all the other students outside.
I don't know how likely you are to get what you want or how likely you are to get shared/single. I think some people choose shared!