It is based on the Pompeii plans from Forno Bravo. 40 inches was the biggest I could fit. Dome is 16 inches which I felt was a good all around hight for pizza, bread and roasting. I like the look of a brick oven as opposed to cast so decided to go that way. Made sure the hearth is well insulated with 2 inch insulation board, dome wrapped in insulation blanket, skim coat of concrete and then will get vermiculite on top and around sides. The Portuguese mason told me that in the old county they insulate with ashes.