Ok. After recently reading the zombie survival guide again, I was informed that one in four "infectees" can climb a ladder. So I had to change my plan a little bit...

So here is a terrible drawing I threw together on Paint. For the time being, lets assume
Blue Line = Staircases
Green Line = Elevator route
Green blob thing (?) = Elevator Car
Purple Dots = Survivors
Red Dots = Infected
Red Lines = Infected Routes

As you can see on the picture, our little purple friends are royally f*cked. Whether it's a fluke or not, eventually the button on the elevator car will be pushed and bring the zombies towards the top floor. And even if the button isn't pressed, the zombies can still climb the stairs and corner the survivors. So how do you keep the red dots from snacking on the purple ones? A barricade may seem like a good idea at first, but it's not worth the valuable time you have because the hordes of flesh-crazed sonsofbitches won't stop pounding it down until the literally deteriorate. So the obvious choice is to break the staircase down. As you can see, this is the one of the routes they can take. The only problem is that upscale apartment buildings have staircases made of steel. So find the $hittiest, dingiest, sketchy-est (is that a word?) apartment building possible! The staircases will likely be made of mostly wood and plastic. Then destroy the chord to the elevator shaft and you're isolated from the lobby. Good job. So now you need to be able to get down for supplies and possibly rescues, if that's what you want to do with your time. So a rope ladder or a retractable one will work well for keeping the zombies away from you.

The only other thing is you might want to expand your 'safe zone'. The beauty of this is that in my town there are something like 3 apartment buildings in a row. So if this plan works well then rinse and repeat with the other buildings and create a makeshift bridge to the next one. Now you have a back up fort. If you can, then just keep doing this with more buildings.

*this plan is only for people who can't go north! The more people there are the more infected will be there*

And that's all I got.