“楼房” is especially different with 平房”，但是，无论是“楼房”“平房”“工厂”“医院” whatever buildings，都属于”建筑“，even the military bases ...

Generally, if you are not going to specify some buildings, you just take" 建筑” , for instance, somebody is asking you way,  you might just answer:  several blocks away, there is a "建筑“ ... but when you try to find a room or a apartment to stay in, you might specify it as " i would like to live in the 楼房， not a bungalow" 

i hope this will help.

hey.my english is very poor.but i still like to explain the difference between 楼房and 建筑              楼房 can live for people.it includes wall and proof    but 建筑 includes more wide range.like tevelsion tower.bridage and so on .all can called 建筑

I think they explain it very uwell. But in my view, 楼房 always means apartment, resident.(but it can also means others a working place maybe and others) eg. 我住在对面的楼房。I live in the apartment opposite us. Then,建筑 is a official word which describes a beatiful and stunning building. eg.这个博物馆是个独一无二的建筑。 This museum is an unique building. Of course  you can say 这个博物馆是个独一无二的楼房。While we do not say the latter one because it is a little  ridiculous and makes others think that you have no common sense.

All in all, 建筑 has a wider range than 楼房。