If I were to point to a building and ask what it was, would it be appropriate to say "あれ は なん です か", "あの たてもの は なん です か", both, or something completely different?
Both are perfectly correct and natural-sounding.
Another word we also often use in these situations is 「あそこ」, which means "that place". You can say:
To speak more informally, we say: