been reading the forums with great interest and this thread is one i can actually contribute to.
I have built one a few yrs back , the most important part is the fire bricks
with mine i also designed it with a floating slab for the oven itself and then an external wall so no one can burn their hands by touching the outside.
i also set mine up with a electric rotisserie so i can do a few roasts etc when im cooking the pizzas.