Just for the record: I just signed up for a WAC gym membership so I can shower while this is under construction. It’s like a State Park in here, except that I have fiberglass dust instead of dirt and sticks stuck to me.
How to get your pre-slope pitch line. stick a piece of material equal to your required pitch on top of the drain and use a level to tet it right. then a level to take that all the way around the shower pan. via, what do you know, john bridge.