This is not to say that the front door of the building you live in does not influence the energy of your apartment. It sure does. The stronger energy the front door of your building can absorb, the better energy is there for all apartment dwellers.
However, in defining the feng shui bagua of any space, we are defining the energy of the space that you are actually connected to and responsible for, thus no need to take the reading of the front door of the whole building.
These tips on choosing an apartment with best feng shui will help you further. And, of course, be sure you know how to take the feng shui compass reading of your front door in order to define the bagua. Good luck!