The trick to getting oddball profiles to roll well is very good fitting dies. So if you are using some wacky profile, you will probably need custom dies. The Italians do a lot of custom window frames in very complicated aluminum profiles, all over southern italy, fitting them into very old houses with curved top windows. They use plastic dies for aluminum extrusions- things like Delrin or UMHW, lathe turned to exactly fit the profile. With thin wall aluminum tubings and extrusions, it also helps to have a
3 roll powered roll- the cheap hand or motorised rolls usually only power 1 or 2 of the rolls. With all 3 rolls powered, you can apply less downward pressure, and get less distortion. Of course, 3 roll powered rolls cost a lot more.
This is probably not a cheap garage project- depending on the size of the extrusion, and the size of the finished ring you want, it could run into serious money. It might well be easier and cheaper to turn these from solid on a lathe. I dont know the exact shape you want, but if they are only 6" or 8" in diameter, and 3/4" finished material diameter, you could probably get someone with a cnc lathe to turn these for a few hundred bucks. A decent roll to roll these is gonna run 5 to 10 grand, with custom plastic roll sets another $500 or so for each size material you need to roll.