I'm always late to the party...
I don't like the idea of galvanized sheet at lowes/home depot. Having both cut a lot of it myself. (New home construction) & used it to make a few things on my car. I don't see how someone would cut it to make a gasket. You could trace cut it with a knife, but OMG the work involved on galvanized steel to do that!?
Cutting your own copper gaskets is easier (I do it on several R/C plane engines I run), and has been done for cylinder head gaskets on motorcycles for a *long* time.
When you O-ring a cylinder head, you cut out where the O-ring sits on the head to give the ring a place to embed. That is a lot of work to be building exhaust gaskets!!!
As long as it's not an actual crimp in a gasket (I.E. a little bending is NOT a problem, but an actual bend is). Don't worry about it not being perfectly flat. You're fine. At worst, supply a can of copper-kote for someone to seal it with. That's boarder line over-doing it in all honesty.
(A life-long mechanic friend keeps swearing to use this GM head gasket sealing spray/goop/whatever. If I could remember the name of it, I'd tell you to have people buy that)