I figure maybe 6 or 7 large size shipping containers, arranged in a geometrical shape, with firing slots cut into them, and barbed wire running along the top edge. sleeping, eating, and other essentials inside, with POSSIBLY enough room for a helo to land (I wouldnt own the helo, but it would be beneficial if we could get word out to a rescue party). then, maybe have farmlands outside the walls, growing primarily rice and beans. not sure where we would get water from, someone help me out on that. 3 tactical watchtowers on top of the walls with marksmen in them, and a warning system inside to warn the field workers of an incoming attack. the program could be run adequetly with about 17-18 people, the more the merrier. keep livestock in a pen inside at night, and let them into the fields controlled during the day. the rice and beans wouldnt provide any cover for the zombies, and they have all the proteins and essential nutrients required for human survival. i figure with regular crop rotation and a steady water source, we could survive for possibly 50+ years. the only problem would be ammunition.
I like the idea of shipping containers (have even seen some people make them into nifty little homes
. The problem would be finding enough containers to make a decent sized compound, and finding the equipment to arrange them as necessary (as well as knowing how to use that equipment, i.e. cranes etc.)
In all practicality, re-purposing an existing structure would probably be the better bet. Less time, energy, man-power, and risk involved when you don't have to create something from scratch. Farming would be tougher to pull off, as you would then need a way to fence off open land...but there is enough existing fencing material to do this. You could scavenge all the chain-link fence you'd need from around town (snipping the metal ties that hold the fence on the poles). Then all you need are some sort of poles, which you might be able to salvage as well, but that would take more work obviously.
It won't be impenetrable, but lets face it, no realistic compound will...unless you happen to find the perfect layout which only requires minimal modification. Then you could spend more time fortifying smaller areas instead of large spans of open space. In fact, now that I think about it, an apartment complex might be a pretty good choice. Many layouts are comprised of several buildings surrounding an open "common space" than could be used for farming/animal holding. The buildings could double as both a living space and a barrier between you and the outside. Then, all you would need to do is fortify the outter-most doors and windows, as well as fence off relatively small "openings" that lead into that central courtyard.
This is sort of what I am talking about