I had mine plasma cut out of 5/8 thick stainless plate. My plasma machine could cut it but just barely so I had the steel supplier cut it and ship the hole also.
Without going and measuring it, what I ordered was .625 inch thick, 25.125 inches in diameter, with a 20.875 inch hole in it. I welded it on, then trued the entire thing in a lathe. That removed about .030 off the face and .125 off the outside and inside diameters. My finished size is just under 5/8 thick with an OD of 25 inches and an ID of 21 inches.
If your going to have yours rolled you will surely have to machine it, preferably after it's welded to you conning tower. It's tough to roll the hard way and keep it flat.
Price it both ways. I made some other parts from the drop ( the hole ) that would other wise would have been made from carbon steel. They look better and won't rust.
I notice you say "hatch ringS." Only my bottom ring is stainless. It's the one that gets scratched crawling in and out. The ring on my cover is carbon steel, also cut from plate, but painted.