How Can I Tool Drain Recess In Stainless Shower Base?

I want to fabricate a custom-sized stainless 304 shower base. (It's for a TINY bathroom in a tiny house so standard-size commercial shower bases are completely out) I can do the welding and braking but am unsure how to get the drain recess or the cross-shaped drain trenches going from the corners to the center drain you sometimes see. Is this something that I can manage to do with a 20-ton shop press or can i just weld a flange onto the backside? As for the cross trenches, i don't know how those get indented.