Okay, I'm going to do something ***-backwards here to save time. I'm at work with no access to my drawing programme, so I'm going to go ahead and post the assembly instructions that go with it before the drawing itself. Of course, it won't make much sense until you can see what I'm referring to. It'll be up tonight if nothing goes wrong.
To start with, the hoop is composed of 4 x 1/64" aluminum rings, two of which (the 'inner' rings) are 12" outside diameter. That is also the size of the 2 'spacer' rings, which can be composed of plastic or whatever and are 1/32" thick. The 'outer' rings are 12 1/4". All have an inner hole of 11 9/16" diameter. The perimeter of the hoop is composed of 3/8" wide steel banding material such as is used to package lumber. You can get scraps from any lumber yard or hardware store, but will have to remove the rustproofing coat (easy). Just make sure that there are no kinks or creases in it. It needs to be 37 1/2" long. You also need 4 'studs', which are 3/32" bolts about 1/4" long with the heads ground down to 1/32" thickness, with 3 matching spring washers and nuts. The hinge plates and latch can be any fairly strong, thin material such as 1/32" aluminum.
1) Tape the band end-to-end in a 12" outside diameter circle (there'll be a small gap) and set it on one of the 'inner' rings. Place the other 'inner' ring on top, so the band is sandwiched between them rather than wrapped around them. Clamp solidly and braze the band to both rings from the outside. Once that's started, you'll probably have to keep moving the clamps and positioning the band as you go. Make sure to keep the outside flush with the rings. At some point, remember to remove the tape. You might also need to heat-sink the aluminum, but maybe not if you're careful.
2) Clamp the 'inner' assembly, 'spacer' rings, 'outer' rings, latch and hinge plates in place. The hinge plates should be centred over the gap in the band, with the latch diametrically opposed. Drill the stud holes. The ones for the hinge plates go all the way through the whole assembly (to ensure alignment). The latch ones just go through one 'outer' ring and spacer, although you can go farther without hurting anything.
3) Unclamp the parts and enlarge the holes in the spacer rings to fit around the stud heads.
4) Put the studs into place from the inside of the 'outer' rings and braze the heads to the rings.
5) Clamp the 'inner' assembly, 'spacer' rings and 'outer' rings into position and braze the rims of the 'inner' assembly to the 'outer' rings with as small a bead as possible. This might burn the spacer rings, but it doesn't matter too much. (Watch for fumes, though.)
6) Cut the 'V' notch for the hinge. You might have to cut more of the banding away if the original gap isn't big enough.
7) Install the hinge plates, using lock washers and nuts.
8) Grind the hinge plates down to match the curvature of the 'outer' rings. (Important!)
9) Cut the latch opening and install the latch using one lock washer and nut on the pivot end.
That's it! (For the hoop, that is.)