Had a slow day at my shop so I designed a fire pit on CAD and fabricated this fire pit. It’s 1/8” steel on the sides and 1/4” steel on the bottom. All cut out on my cnc plasma. More on reddit.com

304 stainless steel is what you want. You're probably not going to find it in a box store though. If you live in a town big enough for a Lowes/Home Depot then you're going to have a steel supply store that will have what you need. I would use angle or square/rectangular tubing as you'll get a lot more strength with less material. It's going to be a little pricey (poking around on the net and I see it for $7 a foot or less depending on the shape and thickness) but it will be corrosion resistant, easy to clean, food safe and basically last forever. Plain steel (A36 most common) that you can pick up at the box store could work because it sounds like you're talking about the supporting structure and not the cooking surface. Plain steel isn't going to leech anything but it is going to rust and make for a lousy cooking surface. It's going to be cheaper but much harder to clean and wont last near as long. This is similar to cast iron except that cast iron will generally develop a better "seasoning" which is basically a coating of oils and residues from cooking which will act as a rust preventative. I'd personally go with stainless so that I wouldn't have to think about weather protection like you would with plain steel or cast iron. Regardless of the material, it's going to have trace chemicals/lubricants left over from manufacturing and could have a rust preventative coating applied. Be sure to use an alcohol based solvent and thoroughly clean the material. Have it sit through a fire or two before using it for cooking. DO NOT USE GALVANIZED STEEL! Galvanized steel is coated with zinc which is toxic, especially at high temps. More on reddit.com

Might wanna radius those shin-destroying corners. More on reddit.com

304 stainless. More on reddit.com