First off, I'd like to say that the custodial parent (if you are the NCP) has NO say in how ANYTHING is done in your home - WRT house rules, sleeping arrangements, etc. And, vise-versa.
Second, I have 4 step-daughters (now all teens) who came back here to live 3 ys ago. We only have a 4 bdrm home. My Oldest BD was already just moved out when they came back here. So, two of the skids got her old room (its small) with a bunk. One s-kid moved in with my other 2 bio-daughters and our 2 boys have a room. The youngest SD has her dresser, etc in the upstairs hall, near the bathroom, but she sleeps on the pull-out sofa bed, because 1) none of her sisters wanted to share a room with her because of her VERY FILTHY living habits and stealing/taking & breaking of her siblings belongings. It was a problem even when the 4 girls lived with their BM... 2) we just didn't have any more bedroom space. Period.
Anyway, now that one SD has graduated HS and is 18.5, when she leaves home, the youngest will get her spot. Basically, because we don't have a huge house and our last name is not "Trump"
we just had to "stack 'em & rack 'em" with bunks.
My OBD, when she vistited her dad almost every w/end, never had her "own" room. She was sofa-city when he lived in apt. and when he got re-married and moved to a house, my BD had to share space with her SM's daughter.
You do what you gotta do and what works FOR YOU.