Well, the tense aside, you could add です, it would make it a bit more polite.
If you are stating information that you got, but which is probably still the case (you saw his house yesterday, and you can assume that it is still the case today), you could stick with the non-past です.
You could also switch it over to past tense and say that it was small and old, but the sentence will then leave some ambiguity as to what the situation is now. In that case, you'd change it to 古かったです。
It’s often tricky looking at single sentences by themselves, since you lose the context of how the information was gathered (are you just stating it, did you visit it yesterday, is the information being given in order to then show contrasting info next).
