Our school is a two-story building with classrooms on the first floor and offices on the second.

two-story 是由数词 two（二）和名词 story（楼层）组成的复合形容词，中间用连字符连接。story 在这里指建筑物的"层"，two-story 表示"两层的"，用来描述建筑物的高度结构。