Heh, well, I don't think it's much of a secret that I probably only use about ~5% of the possible textures habitually, if that. As for square hangar, towards that end I was thinking I wasn't going to have a hangar at all because I figured I failed at boss fights. I literally built it in about ~3 hours and left it like that because I was so happy with how the gameplay turned out. You'll notice I forgot a few things.

If you look in mapster, there's a whole giant sector behind the brown wall to your right as you enter the hangar. There were supposed to be pipes and machines behind a grate there but it completely slipped my mind! Doy.
Edit: actually, if you look around a little more in Mapster, you can see where I left some old sectors off to the side. Most of them were just temporary sectors I used to rotate groups of sprites, but there's a sideways-T-shaped texture that is possibly the oldest remnant of the map with a decidedly more gritty feel than the rest. (It's half-textured, heh.) I built it in the first days after FOS Station, about the same time as the starting U-shaped corridors and ramp, and it was my original plan for the aesthetic feel of the level... (it would've joined the rest of the map just after the giant split-door just before the hub area; in fact, that short corridor between the silver door and the hub was part of the original plan, and you can see the angled frame survived).