If a building is used frequently and I'm going to have to describe people moving from place to place within it, then I generally make a floorplan in the same way I make maps for outdoors areas, to keep everything straight in my head.

I didn't make a floorplan of the Coral Palace until after my first draft was completed. I found it impossible to do revisions and add descriptions (I always need to add descriptions to my first drafts) without one, however.

Architecture I don't think I'm so good at, sometimes it helps to try drawing the buildings and see what they would look like, but mostly I think that my verbal descriptions look/sound more interesting than the pictures.