Diferencia entre 层 y 楼

 Hola

层 could either be used to describe an exact level of building or the total number of levels of a building.
e.g. 我家在第5层 | 这栋房子总共有7层

but 楼 is only used to decribe an exact level
e.g 我家住在第5楼
it will be a little bit weird if you say 这栋房子总共有7楼 

If count the floor,we can say the building has 30层/楼。
I lived in 5层/楼
but if the refuge layer or fire escape layer ,we say 层。指专有名词。
ex，第18楼/层是避难层。 第20层/楼是防火层。

The two words mean the same thing, but they are used in different places. 层 refers to how many floors a building has, or when you take an elevator, which floor you want to go to.

你要去第几层?

 楼 can be used as a noun. For example, there is a building here. 

这里有一栋楼

When used as an adjective, it is very colloquial and the meaning is the same as 层.