Stacking rocks in this build is a time consuming, but necessary skill to master. For those of us from the Tetris generation, the interlocking placement of stones to build the walls of the oven can be a nostalgic trip down memory lane. Good luck to everyone else.
An abundance of rocks in a variety of sizes and shapes need to be at hand before beginning on the foundation. If possible, use the largest stones at the base as this part of the three walls will be supporting most of the weight. Fit the stones together as closely as possible when stacking. If necessary, natural clay or soil can be used as mortar and/or filler.
The length of your walls is largely dependent upon the size of a ledge and capstone. The larger your available stones, the longer your walls. The height of your walls up until the ledge stone is placed should measure between 8 to 16 inches.