High windows. Most houses have ground floor windows that are at waist height. When the windows are located at least 6 ft off the ground, breaching the home becomes more of a challenge, and defense can focus on doorways.
Inside the home, regarding floorplan, I'd say the most important factor is the owner's knowledge of the layout's strengths and weaknesses. There has been discussion of "choke points" above, but these can work equally well to the attacker's advantage. It all depends on who gets to them first.
Talking about a defensive floorplan is, to my mind, like talking about the design of your "dummy wallet." If you're carrying around a wallet to be handed over to robbers, then you have conceded the game in advance. All effort should be on the prevention of unauthorized entry. Once they're inside, it's down to a matter of seconds only.
If your tactical planning involves shootouts inside your home, then you are thinking wrong. The inside of your home is not a freefire zone where you plan to be standing in one area, pumping away with the shotgun, whilst the attackers are befuddled by the clever design of your stairwell or somesuch. Although some do get lucky in this regard.
Rather, most accounts involve running, hand-to-hand fighting and life-or-death struggles over possession of the firearm. It seems like what really matters most is being able to get to a firearm quickly and bring it into use. They'll be right behind you, if they're already inside. If they're outside and attempting entry, then you can barricade, defend the entryway, etc. So a strongly defended exterior is really 99 percent of the game.
