How to rough in framing for a custom fiberglass shower pan

John, a great deal depends on which pan you buy. I install Swanstone pans which require no framing at all after the walls are framed. The pan sits on the floor in a bed of modified thinset. http://www.theswancorp.com/images/link_installation/Shower%20Floors%2006-10-09.pdf

A method gaining popularity around here is to use a fiberglass resisn to create the pan, using multiple layers, sort of like a hot mop pan would be done with tar. IT's then filled in with mud and then tiled. Is this the sort of pan you are talking about?