[jeff]

Mieno,
That's scary: Kiko Denzer was my first read also. In fact, his book [library loan, eh], is beside me as I chook-pick the keyboard.
Then came Russell Jeavon's little gem, "Your Brick Oven". The man is a crow-eater, but an exceptional one. (In fact honorary Cane Toad title may yet be offered.)
Along the way, from "Kiln Building" [Ian Gregory] to "Stuffing Stray Cats" [Anon], I was offered FornoBravo site by a local brick manufacturer. They also offered a Brisbane feller, who's address I'll try to find for you later.
But to answer your question, the plan was for 27". Things, (mainly FB), persuaded me to add a few inches, but I abused my brick gauge, so 30" grew to 31", while dome height went from 440 to 500. (Sorry to mix systems. God alone would know why our Cousins stick with semi-Imperial measures.)
Mieno, I've tried to stick with standard oven ratios, but have strayed a fair bit wrt materials and timing (of firing). Only time will tell, but rest assured I have found it a brilliant exercise.
Best I stop.
May your Christmas be fine, and 2008 fantastic.
Jeff.