G-Man, what he means is that:
1) Make your level with some degree of realism in regard to how the rooms are laid out. EX: Imperials aren't stupid enough to put an armory right next to a cell block, in the event of escaped prisoners.
So that it might be laid out like a real structure of a similar kind.
2) Make sure each room has a function that it would normally be used for. Architexturists don't go designing houses with empty rooms. EX: Even if you're doing just a, say, run-and-gun level through an imperial facility or something, you'll want to think about what kind of rooms they would have and then try to make a realistic floorplan and work from there. Of course the floorplan should be largely inspired by your plot as well.
3) What does the room's architexture need to look like so that it looks like a room of that type? What 3dos will I need, etc. EX: A living room should contain a couch 3do, a couple tables, a few lights, etc. An imperial cellblock could be designed, architexturally, after the Death Star cellblock.
4) Is there anything extra I want the player to be able to do in the room (ie turn on or off a lightswitch, solve a puzzle to get a key, etc) and is it realistic in terms of the plot? EX: Even little puzzles like finding a key can help keep the level from feeling too linear and repetative (Oh look an enemy, zap, dead. Another one, zap, dead. Repeat x1000).