Ok, now I'm understanding this dam thing. I thought that was a curb, but I just googled rubber dam. My main goal in this is to have all water run to the drain and never get stuck on the outside of the shower if someone forgets to shut the shower curtain, or whatever. We had a low spot on the outside of the shower and in that area the subfloor has rotted about a foot in diameter, but not the joists.
So I'm trying to prevent that water collection problem. I like a continuous slope without a lip to catch and hold water on the outside of the shower. I've had one quote and he's trying to talk me into a pan again, because of leaks. But, honestly, that didn't help us here. Thanks! And thanks for the correction 1/4" per foot helps.