Could you please show me how to build a shower floor out of concrete and reinforcing iron?

I can't do any better than this guy so here is his site How to Build a Shower Pan Why do you feel you need iron reinforcemnet? Most pans are lumber, membrane and mortar.

You could always use the schulter system. It has a styrofoam floor with a waterproofing membrane and comes with a drain. Available at Home Depot

Schulter is the maker of the Ditra sub flooring material I have used when laying ceramic tile on concrete. Ditra works great so maybe their Kerdi drain will work as well.