If it were for me, I'd much prefer polished aluminum/stainless sheet.
Carbon steel would be my second choice. I have a pattern I made to duplicate the guard that came on my Sears bike. I'm going to attempt to fab one with thin aluminum sheet.
Fold on the dashed line (and fold the bottom tab over), then the long piece bends to match the front curve and attaches to the tab.
You could just square or angle the front as well.