I built a pompeii oven last summer and there are a few things I would do differently. First, I would build it with a lower dome height (for a 36" oven floor, go for a 14" dome height; I built mine to 18".) I would have ordered all of the material from forno bravo. Once it came down to it, my costs where a little higher than what they sell the kits for (excluding shipping.) The big advantage is that everything is included as opposed to having to run around town and gather the various materials. Make sure the block stand is high enough. I didn't include one of the half-height layers they suggest in the instructions and It ended up too low. You might even consider adding an additional full-height row so the oven floor is right around the height of a mark just below your chest.
I'm sure there are other things, but that's what I can think of off the top of my head. I wish you luck.