Yeah, I cut a 5’ piece of 1x12 to the radius of my arch, and then I would bend a little at a time and check it against the pattern. Doesnt have to be millimeter precision, just pretty close. Also, there is a straight leg 26" long at the base of each arch, to give the structure better headroom while maintaining a 5’ radius.
The end wall did go up first, and you cant really see them, but I ran a few 1/2 pieces of EMT across the back to support the panel edges. I hammered the ends flat, and then screwed them to the frame. Once the back was covered, I just trimmed them to the curve with an angle grinder.
It is sitting on 10 concrete footings (8" diameter footing tubes). I made short sections that I slit the bottoms and splayed open so they would anchor in the concrete. Those short base sections could then be cut level. The structure itself then sits on the tubes and is joined with little emt unions. Since the unions are not very strong, the metal siding laps down over to the footing tube, and that should anchor it pretty well.
This design would probably need to be modified for high wind and for snow loads - we have neither. A 40 MPH gust of wind here is a rare (and scary), and my little valley is fairly sheltered from the wind. I was thinking that for snow you could make the structure a bit taller, then zigzag some aircraft cable back and forth between the ribs near the ceiling. That would act as collar ties, and prevent the thing from crushing like a pop can under a large layer of snow.
Yes, you are spot on - only I used much less concrete. I had the footing tubes on hand, so I think I spent 25 on the footings. I only used 5 bags of concrete. Also I will add to your list that I used 4 sticks of 1/2 EMT to shore up the back, and you will need 15x 3/4" EMT unions (25 for $10). Otherwise, the difference seems to only be the regional price of materials.
The design was a simplified version of my greenhouse, which I built using the same arches, but with complete end walls, and a covering of clear plastic. It has held up pretty well, although its frame is also a bit more sophisticated. It is screwed to a base of 2x6’s and has not been blown away yet. the curved sides probably help with wind.
If I were to do it again, I would probably enclose the entire back wall - originally I had thought i wanted a vent so I could burn inside and let the smoke out, but I am not thinking that will be very practical. In that case, I should have used 8’ panels stood on end along the back, and then trimmed to fit. It was a fun project though, and you can keep an eye on how its doing the background of all my future charcoaling pictures, although I will probably block it out of frame if it falls down