Ok I built a small kiln for you guys as an example of how to build my version. There are no plans and you dont need them. You just need to understand the basic principal of it and you can scale this as big as you want. Here I built a small unit out of a 5 gallon steel bucket and a 10 gallon steel drum.
The basic construction I came up is very simple. You simply use threaded to fasten this system together and I used some steel 1 inch square tubing as stilts to hold the unit up so that you can fit a catch bucket under it to catch the charcoal as it is produced
For the grate I just bent some 3/8 rod into a triangle to fit inside the fire tube and rest the ledge. This is all you need for a grate, it must a very passive grate in order to allow the charcoal to fall through as it become brittle enough.