All custom built showers require a pan or receptor to keep water from rotting the wood under and around the bottom of the shower. The most popular pan/receptors are acrylic/fiberglass/Swanstone (which cannot be tiled), copper, or PVC.
The shower curb is the most vulnerable component of a custom made shower. Water will find its way to any unprotected surface. To overcome these shortcomings, I use a PVC pan liner that I install on top of a mortar base, slopped to the drain. The drain I use has weep holes that allows moisture that reaches the pan to run into the home's sewer system. Since these liners are flexible, I install them so the sides are higher than the curb's height and most importantly the liner is folded over the curb, which prevents water from reaching the structual components of the curb (the most common reason a shower with a copper pan fails).
The following pictures show some of the rotted curbs I've encountered when removing copper pan showers: