Out of curiosity, why does it matter about the internal size of the house, bearing in mind that the internals rarely bear any resemblance to the exterior views in-game?
I am assuming of course, apart from spending a few (relative) trues and then designing a castle, so getting a better place on the cheap., or
A larger internal house will obviously be Kb-wise, larger than a smaller one, but give the size of servers nowadays versus the number of players, I would not have thought that would have been a problem.
I can't think of any other reasons, so hopefully someone more enlightened that I am will know. As I say, just out of curiosity, really.