My husband and I have 3 kids (F4, F18, & M20), and we live in a 3 bedroom house. The youngest one used to stay in our room, but this year since my daughter got accepted to college we decided to turn her bedroom into a room for our youngest.
When she moved out we put her stuff into the basement. She took all her important stuff to school. The only things we put in the basement were a bed, and a closet with stuff she wasn't going to pack. There's no way to make the basement a bedroom for people asking that.
Her older brother is out of the house, but goes to college close to home, so he comes home almost every weekend. We let him keep his room.
She just came back home for a few days for the first time since leaving, and when we told her she had to sleep on the sofa she blew up at us and called us a**holes for taking away her room. We had told her we might end up doing this a long time ago, and even then she got mad and said we shouldn't take her room