EDIT: I meant to quote someone but whatever.
I also happened to take inspiration from some of the photos posted, it has never occurred to me that I could make a space for the 4x4 inside. Usually I just park it outside, out of the way of potential zombies, and hope for the best. I actually had an even bigger design in mind, but I realized it was going to be too time consuming. Originally, it was supposed to have an L-shaped tunnel. The inside corner would've been its own room (eventually a tower) and would make a nice cube. If you ever played Halo 3, there is a map called Rat's Nest, in the end it was supposed to be reminiscent of that.
I settled on a "garage" type of look, which I think came out rather decent. I still need to decorate the interior and roof areas some more, but the outside perimeter will probably stay mostly the same flat cube. I usually don't like flat, but its hard to work on the walls when your ten blocks in the air with spikes directly below you lol. Also, no lighting because I haven't found the schematics for them yet.
Will try to upload some screenshots, just gotta take them first.