Unless you're in Downs C (which has the common room/wash room on the ground floor, so everything is a level higher) 5 is on the bottom floor, but not at the very bottom. If you've visited, you'll know what I mean...there are 3 kitchens, and three floors which are each split into two sections. You'll be the higher section of the bottom two floors. They do put girls on the ground floor...there was one there when I lived there.
The A bit doesn't mean anything, unless it's a shared room (which in Downs, it won't be).