Blender - Adding extra face on cube to use as a door

For my game I am modelling a lot of different buildings. And all these buildings have something in common..Doors and windows. But each time i make some kind of building it is pain to cut the doors and windows out of it. Instead of doing that can I just prepare 2 faces- one for door and one for window and add these on the main building cube? Does it have any negative effects in unity loke the performance?

 

Yes, you can do that. The performance impact will depend on how many vertices you have in comparison to both methods. When I make my models in blender I tend to make them in sections. I do this so that in unity I can make a lot of different configurations of the same thing but it will look like a unique object in game.