A couple quick thoughts: I think you need a double floor - two ceramic layers with an air gap. I think you will brun the bottom of the pie to a crisp if a ceramic deck is directly over the fire/coals assuming the fire is hot enough that the device gets you to a meaningfully fast bake time.
I'm worried that an uninsulated ceramic dome will not maintain enough top heat. You will need a meaningful differential between the deck and the dome with the dome being the hotter.
Yes, Iíve considered both of your point to some extent. I found pizza by way of my Big Green Egg (BGE), a ceramic grill. What you described is exactly what the ceramic community recommends when cooking pizza in an grill like this. With this setup you would use a ďheat shieldĒ, or plate setter as the BGEggers call it. This deflect the initial heat from the coals so that point is covered. My apparatus sets above all that.
As far as the dome retaining sufficient heat, all I can say is that is should retain as much as the BGE dome retains. This issue actually strikes to the core of why I wanted to take on this project. Contrary to the common conception that ceramic grills contain convection waves within the cooker I now suspect that there is actually very little convection occurring within these cookers.
Donít get me wrong, Iím a huge fan of the product, but as a smoker. It doesnít have the convection airflow needed to heat the top of a pie. We put together a virtual model in SolidWorks (a drafting and design software package) that has an airflow simulator feature to simulate airflow within a given structure. We found that most of the hot air simply flows along the walls and straight out of the chimney at the top.
This would explain why ceramic grillers are told to put the pizza stone as high up in the dome as possible. It has to be high because the only heat the top of the pie gets is the radiant heat from the dome walls.. no convection heat topples back down as heat is rising from all directions and the exit is straight up the top.
Even though this dome may not get anywhere near the same insulative qualities as a brick oven, it should get significantly better use of convection heat in the ceramic grill.
Iíve included a couple of links to pics Iíve done on the Egg. Iím hoping that with this new setup Iíll actually be able to accomplish what you guys seem to refer to as leopard spots. ;0)http://sphotos-h.ak.fbcdn.net/hphotos-ak-prn1/v/711520_10200264419193827_767044004_n.jpg?oh=3bcf60de0d6206077c26150e963694f9&oe=50F6BB0F&__gda__=1358396925_add490cca5f287850529a5eabd762373http://sphotos-h.ak.fbcdn.net/hphotos-ak-snc7/v/565690_10200264419353831_918209847_n.jpg?oh=a1e72f4c9f6f8d877d32e762ea14ec5c&oe=50F69913&__gda__=1358397689_0b9f2ed5d83bfcebfdff3b5abcd0f73c
BTW Craig.. Iíve been trolling this forum for some time and I have to say, Iím a big fan of yours.. One day I really want to build a WFO in my backyard.