PLEASE NOTE: This post is a draft. I have not yet built this kiln but I have purchased the steel and will build it this May. So, I have not tested the below drawings. Use these drawings at your own risk.
The original designer of the Pennsylvania posted this video: https://www.youtube.com/watch?v=j8aN3A3a8FU
Drawing 1. Basic Dimensions.
Note that each piece is bent outwards at a 90° angle at the top and 45° on the sides. The top bend increases bending strength and the side bends provide a surface for attaching the sides to each other. I will drill holes and attach with bolts, nuts and washers (heat-resistant) so I can disassemble the kiln and move it myself.
As the above video mentions, the design suggests 1/8th-inch steel.