Any of you who grill pizza find it delicious... and maddening, as the toppings rarely cook as thoroughly as we'd like while the crust burns. The cure, as explained in many places on the web, is to get heat radiating from the top.
The Genesis, along with many subsequent Weber (and many other brand) gas grills, has a 24" x 18" grilling surface. So I purchased a like-sized, 3.5" deep steel pan at a restaurant supply. You can get them on the web for like $35 shipped. That functions as the 'top' of the pizza oven.I also purchased a dozen 1" x 4" x 8" firebricks, a piece of 12" x 24" expanded steel, a 12" x 18" weldable steel sheet, and an 8" x 24" weldable sheet. I chiseled the brick, bent the metal, and put it together and burned it in yesterday. Tomorrow will be the first experimental pizza.
I'll take some pics and post 'em to show how it's put together.