if the concrete base is already poured, drill holes 6” deep and install with epoxy #4 rebar at least 5’ in length.
Use air to clear the holes of dust.
Use Epoxy to set the steel
Use rebar caps for safety.
Set horizontal steel every other course, especially in the West.
On the fifth course, use half blocks with open end.
lay #4 rebar grid with metal lath on that level
pour concrete in the walls and the base at 6” with another grid of steel.
Use wood to hold up center of grid until concrete has set.
Pour 6” of sand on top of concrete. Use construction paper if concrete is wet
Another layer of paper over sand, then another layer of concrete at 4-5 inches.
Whatever Oven you choose to build on this Masonry Structure, as a Stone Mason, I consider this to be the best and easiest method available for Masonry Wood Fired Ovens. Have Fun and Buon Appetite.