How to set camera top of the model?

I have some models of buildings that differ in size. Some have suppose 30 floors and some with 10 floors. What I want is to set the camera position to the top floor of the model but if I set it for one which has 30 floors it will not work with the model which has 10 floors. But I want it to work for all the models no matter how many floors there are. How can I achieve this?