Well, firstly the answer is
an empty room
I feel like I have seen this before, not the exact clues obviously, but the general gist/answer. Can't remember where though, sorry.
For what its worth, I like your clues; not sure how you'd improve them (not the least because "improve" is subjective). Perhaps you could explain what you mean by that?
Otherwise, if it were me, I'd try to make the couplet follow some form of rhyme scheme, but thats just because i like rhyming riddles, so your milage may vary
Update (just to make it official advice):
@JMac has mentioned in the comments below that its entirely possible for buildings to exist that have no empty rooms, and some tightening up of the wording of the first line might help account for such.
Its kind of a edge case, sure, but that sort of technicality is sort of the heart of a riddle like this - after all, if it wasn't an unusual case, it would be obvious and not a riddle at all!