room with (one)
To share a bedroom in a house, hotel, dormitory, etc., with one. I was planning on rooming with my best friend when we started college, but then I found out that he had rented an apartment by himself. I'm rooming with Janet when we travel to Las Vegas to keep our costs down a bit.
room with someone
to share a room with someone, as in college. I need someone to room with me next year. No one wants to room with Kelly.