Making miniature helmets from copper?

I have, for some time, had an interest in making miniature helmets
from copper. I’m thinking about two inches wide, rather small. My
understanding is that you would have to hammer it into the shape
from flat. How do you go about determining the thickness of copper to
start with? Any thoughts are greatly appreciated.

Paul Anderson

Why not use copper metal clay? It’s very inexpensive, easy to work
with using few tools, easy to fire, and strong enough for this
non-wearing usage, IMHO…