Use What You Have

Earth ovens do not have to be elaborate in design. In fact, by their nature they should be simple.
The person who built the attractive oven shown did not have stone on his property for a base, and he didn't want to buy concrete blocks. He did, however, have wood, and that's what he made the base out of. Wood doesn't last forever, but what does?
He did make one serious mistake, however, by not insulating under the floor. This is more important than insulating the dome, and he didn't do that either. You want a pizza oven to heat up quickly and at least retain some of the heat. Under his firebrick floor he has about 4" of dense clay, and it really takes a while to thoroughly heat that mass for pizza making. He did in fact complain that his pizzas were not baking "right" on the oven floor. Had he simply insulated insulated under the firebrick and forgotten about the clay under the floor, his oven would have heated up lots faster. Yes, he should have insulated the dome as well, but for a pizza oven, it's not as important.