I'll see if I can dig up some pics, but here's it in a nutshell.
Center ring was glue-screwed from 3 layers of plywood (3/4" off the top of my head). This was about 3' outside diameter, with a 2' diameter hole in the center. Simpson sheer hangers (2x4") were put around the circumference to accept the rafters.
Rafters were 2x4's (10' off the top of my head) with 3/8" hole drilled about 18" from the tail end, with a slot to the side for the tension cable to reach the hole. Tension cable was about 3/8 stainless cable. Used about 18 rafters, with the tail ends apart by about 2'.
Assembly
Center ring was temporarily put on a post about 3" above the theoretical final roof height. Tension cable was cut, the clamped with 4 clamps to the proper diamter and laid on top of the bales. 4 rafters were laid on top of the bales, then brought up one at a time to the center ring and screwed into the Simpson hangers. After all the rafters were up, the tension cable was inserted into the holes drilled near the tail ends and wired in so they wouldn't slip out. Fingers were crossed, and the center post was pulled out. Rafters adjusted as need be to keep everything mostly even.
I covered/stapled tyvek (white side inside) to the rafters as tight as possible, the clear plastic, then a tarp. This sufficed for the first couple of months. Took off the tarp, stapled some strips of carpet on the roof, then threw up about 12-18" of straw as even as I could. Another layer of plastic, then the tarp goes back on. Huge, huge difference with the straw up there, but damn if it wasn't a huge fire hazard. Cheap though!
Door and windows used 10" bucks with angle brackets. Plastic on both sides of the windows in summer, with some mosquito netting stapled on. Used a sheet of plastic for a door for a couple of months, then put in a plywood door with plexiglass window.
Plastic on the floor, then tarp, then dumpster-dived carpet padding and carpet. Eventually put in a barrel stove going out one of the windows.
Hovel sweet hovel, but sometimes I really miss that funky little place.