Solid base to build on. It ends up very heavy!
I used concrete blocks and then made a steel frame and poured a concrete pad on top.
In the middle area where the base of the oven will be I a poured a concrete/vermiculite base about 30mm thick to act as insulation for the stone.
next step is to create the chamber
Step 1: The chamber
For this I used Blue engineering bricks, type A are the only ones good for this sort of heat, you don't need firebricks (they cost lots)
I used about 200 bricks, got them for about £60 off ebay
the mortar needs to be high temp, so a mix using terracotta clay sand and cement was used, it goes off but gets harder when fired.
as you can see i created a form using hardboard and ply. I bought the clay from a kiln/pottery suppliers. It needs to be high temp firing.
As you can see from the second 2 photos I have created the chamber then used regular bricks backed by firebricks to make the opening on the front, I used a form for this brickwork as well.
There is a special dimension for the opening, The height of the opening needs to be no more then about 70% of the height of the chamber otherwise smoke comes out and it needs to be wide enough to allow good access.