Number + 楼
楼 (lóu) is a measure word used to count the floors or stories of a building. For example, 这楼上 means "upstairs in this building." It can also function as a noun meaning "building" or "tower."
我住在三楼,每天都走楼梯。
Wǒ zhù zài sān lóu, měitiān dōu zǒu lóutī.
I live on the third floor and take the stairs every day.
他的办公室在二十楼,必须坐电梯。
Tā de bàngōngshì zài èrshí lóu, bìxū zuò diàntī.
His office is on the twentieth floor, so he has to take the elevator.
请到五楼会议室开会。
Qǐng dào wǔ lóu huìyìshì kāihuì.
Please go to the conference room on the fifth floor for the meeting.