You would use a UOM conversion from pounds to sheets. If you are buying to stock, this will get consolidated, it won’t be by job.
Are you buying the steel to stock? Or directly to the job?
One way to get the steel separated is to use planning contracts. If you set up a planning contract for each job, and then set the steel to come from the planning contract, you can have little mini warehouses of separated inventory by job. You’ll get separate suggestions, and you can move things in and out of the planning bin to “Allocate” it to the job.
Really the biggest downside to that is that Planning Contract bins are the same as inventory bins, so you can’t have it in a physical location, and a planning contract bin location at the same time. They added the ability to have more than one bin on a planning contract, but they are still planning contract specific bins.
I made a customization that would create the planning contract, and the bin to go with it, and tie it all together with a button click on order entry. It was nice for ordering long lead time parts before we had the job in the system since the full BOM wasn’t done before they needed to order the parts. The steel we just kept min and maxes of and didn’t use planning contracts for that.