楼

楼 (lóu) is a noun that covers both 'a multi-story building' and 'a floor/story within such a building.' Chinese collapses two English words into one — context tells you which. 那座楼 means 'that building'; 我住三楼 means 'I live on the third floor.' Two things trip up English speakers.

First, Chinese floor numbering follows the British system: 一楼 is the ground floor, 二楼 is what Americans call the second floor. Second, 楼 by itself usually implies a building taller than a single house — for a one-story house you would say 房子. Common compounds include 大楼 (large building, often office), 楼上 (upstairs), 楼下 (downstairs), and 楼梯 (stairs). Register is neutral and works in both spoken and written Chinese.