I've finally finished the building of my wood fired pizza oven. It took a while to put everything together however the final outcome has been completely worth it. I started by laying a concrete slab 155cm x 175cm x 10cm. The materials were sometimes tricky to find however generally I found them at hardware and oven refractory places. I placed 12mm rebar steel placed 25cm apart within a frame made out of pine. The rebar needs to be lifted off the bottom gravel with some stones or pieces of brick. I mixed concrete at the ratio cement : sand : crushed rock as 1:1:1. I used this mix as it was recommended to me however upon investigation it appears the recommended ratio is 2:2:3 or 1:2:4 (Cement:Sand:Aggregate) depending on the source. I think it's best to go by what the instructions are on the cement bag. In any event even with my mix I haven't seen any cracks or had issues. I used about 8 bags of cement all up. It's a lot of work mixing the cement by hand so some sort of mechanical cement mixer is really necessary.
Throughout the build I referenced various blogs and forums found via google for troubleshooting issues. I particularly benefited from this wiki started by members of one of the wood oven forums. Pizza oven wiki
I allowed the concrete to set over a number of days by covering it with plastic and wetting it every 6 hours with a hose. Apparently if the concrete takes longer to dry the end result will be harder. After setting I laid out bessa blocks dry to establish the form of the base of the foundation. I left space at the front top level to place a concrete lintel. I placed 12mm steel rebar in the centers on the bessa blocks and poured concrete to fill the walls. I felt this method would be easier than laying the blocks with mortar.