Old imagines and videos of the apartments
(Try to find vid's and pic's of them on the wiki if you can.)
The top of the apartments was arguably the safest location in game, as it's nearly impossible for zombies to navigate all the way up. Even intelligent zombies will have a hard time with this one. It's also Patient Zero-proof, as you can just leap off if Patient Zero comes. And if a horde were to build up at the bottom of it, there's no need to worry about a zombie glitch-jumping upwards. They'd be inside the apartments, as there are basically no walls.
On the other hand, the apartment was really REALLY hard to fortify. It had a ton of open holes all around, and the first and second floors where easily reached by zombies. Trying to get on the roof wasn't very easy either.