My question is as the title. To make my question clear, the 楼 in the context is not referring to the floors of a building, such as 我住6楼。It is referring to those such as 岳阳楼, 黄鹤楼.
After searching online, I think 塔 is a kind of 楼 when it is built inside a Buddhist temple. But I don't know whether my understanding is correct or not.
In many Chinese people's minds, 塔 are buildings with triangle shape, and 楼 are more flat, which is usually true.
While, if you are into the formal differences in terms of architecture. The difference between 塔 and 楼 is that 塔 has Sōrin (which is the vertical shaft which tops a Japanese pagoda, whether made of stone or wood) while 楼 does not. Certain 楼 may have a triangle shape but does not have Sōrin is called 楼, such as 黄鹤楼. And any architecture with Sōrin is called 塔，even it has only one floor, such as 山东历城神通寺四门塔。
Please note that this definition may only suit traditional Chinese architectures, and may not necessary fit our naming for modern architecture such as (Eiffel Tower).
I think we can call any kind of sharp triangle building as 塔, no matter it embraces any floors within. Like 灯塔, 艾弗尔铁塔, they don't have any floors within.
If 塔 has floors within, we can call them 楼塔.
Another point might be that when the building is more flat(not very high, stiff) just like 岳阳楼, 黄鹤楼, we tend to call them 楼. If it's high and thin, we tend to call them 塔, 塔楼 or 楼塔.
