Difference between 室友 and 同屋
I live in north, we only use 室友, when I see your question, I have to check dictionary for 同屋( I have never heard of it) to make sure I know it right, cuz we can not rely on the literary meanings, for example 家里那人 refer to husband or wife, not any other family members.

You would better avoid 同屋, because that is a slang, they always have other meanings in different areas. For example 同一个屋檐下 usually refer to neighbors, relations but not rootmates.