楼 (lóu) / 大楼 (dàlóu): This means a multi-story building. A `大楼` is a “large building,” and is very close in meaning to `大厦`. However, `大厦` often implies more grandeur, prestige, or height. You can call a large 10-story university library a `大楼`, but you might not call it a `大厦` unless it's particularly impressive architecturally.