Ellen,
Are you upset that he hasn't done it before, or that he is doing it? In either case, he will need your support to finish the job. you may want to pick him up a remodel book that shows pictures, and instructions.

The drain should be a 2" pipe with a p-trap, vented within 60" of the trap.

You will find it easier to use a preformed shower "pan" for the floor, and then either tile the walls or use some sort of solid surface. Solid surfaces can be cultured marble, laminate or acrylic panels. These are glued over "greenboard".

If you use tile, the choices are many. Use a good quality backer board like Wonderboard, Redibacker, Durock. Standard tiles sizes are 4-1/4" and 6"
6" tiles have fewer grout lines and look very nice. There are tile supply stores that will also rent the tile cutters.

Make sure you install a pressure balanced shower faucet. These mainly come in one handle faucets at this time. There are the rare two handle pressure balanced faucets (still hard to find) at this time. http://www.terrylove.com/faucets.htm

One piece fiberglass shower "stalls" are fine if you have the room "gutted" and have a large section of the outside wall off. I doubt that however that is the situation. Most of the time, you will be building the shower into a three sided enclave.

I recommend having a glass company install the shower door when you are done. I don't like many of the kit glass packages. The glass company installer will make sure that the proper sill and sweep if needed, is there and done right.

Good luck, and remind him that he is doing just fine.
Best regards,
Terry