But if I want to follow the standard Portal/Portal 2 theme with a vast amount of different sized squared tiles, I have to cut some of my walls, ceilings and floors into a lot of brushes. Some of my rooms are made up of 10 or more brushes per wall, making for a total of 60+ world brushes per room. Something tells me this is really bad performance-wise and thus the question, can I make such a room into a single func_detail instead and just seal it up into a box?

Example:

Or is there some other way I could go about this without making the poly count go mad?