So I've come farther with the server room designs. We're also in talks with another provider in the colo we're in. It's good to keep a fallback plan.
The new design is an 8'x16' room. We'll be using 2x6 joists (boards in the floor), and we're ditching the cement blocks to raise the room any farther. 6" up is still more than we require for running water. If we have 6" of standing water, we have bigger problems.
The new room allows for 4 racks comfortably, plus room to move.
I found a good source for cooling information. It basically said we'd need about 24k BTU's. Home Depot sells window units that size for $399. Two of those would give extra cooling, plus enough redundancy should one fail.
So, I'm sitting on the plans right now, to see if we're going to start building next weekend or not.