There isn't really enough room for that. The floorplan I have to work with is very small when you consider that most of it is taken up by a large central spawn area and the requisite obstructions that stop you shooting through the barracks. That leaves very little room for any sort of overall structure. If I make it half concrete half something else it's going to look silly, because it'll look like they got halfway through building a bunker and then ran out of money. I don't think the NF would have all their structures half finished or half-restored. I was thinking concrete with metal panels on it for reinforcement, because metal has different physical properties to concrete so using both would give you more resistance.