When I hear “riesiges Gebäude” I don’t necessarily think “very tall”, I think “huge” or “enormous”…like…not necessarily the tallest building in the landscape but the most imposing. Typing this into Google image search actually turns up mostly buildings that are wider than tall, which fits with my intuition.I think this sentence could be improved as a result. Maybe “massive” would be a better translation too.
Also I think there is a second problem in this sentence. “Was ist das für…” seems to be asking: “What kind of (…) is this?” which is subtly different from “What is this?”
If I were translating this, I would translate it: “What kind of enormous building is that?” which is close to what Google translate gives me: “What kind of huge building is that?”