Here you go, Mr Fig Jam's wood fire pizza oven
Not exactly sure if he did it this way but I suggested and adding layers of steel mesh, insulation and concrete over the sand mould. He did say the first internal layer was about 100mm thick

LOL I told him he should have used some darker colour bricks for the arch
So he tells me
50 fire bricks cost $150
Chimney and top hat $150
5 x refractory cement $400
Lime stone bricks he had on hand