Our classroom is _____（在顶楼）of Building A.这句话应该用 on the top floor还是at the top floor

正确的介词是 on ,比如
on the first floor
on the second florr
on the top floor
正确的表达方式是
Our classroom is (on the top floor) of Building A.
我是加拿大人,前英语老师.
英语是我第一语言.