Removed a 5 ft tub to install a tiled shower with mud built shower floor. After removing tub, discovered that drain line running from tub p-trap is about 2-1/2 inches below top of slab, acutually partially encased with concrete. Want to relocate drain to center of shower, about 2 & half ft. That would put drain line, with slope, about 2 inches, or less, below top of slab. To accomodate new shower drain (depth of plastic housing), it appears I'll need to place the new p-trap deeper into dirt below the slab (old p-trap was attached directly to drain line and it's depth was fine for the tub). Will placing the new shower p-trap a few inches deeper into the dirt, below slab, create a draining problem as long as the top of the shower drain is higher than the new extended drain line.
The outlet arm of the p-trap needs to slope at 1/4" per foot to the next connection. If the water has to flow up to get out of that arm it will accumulate crud in the trap and clog. It probably would drain slowly, which isn't good for a shower, either.
You might want to check out www.johnbridge.com for your tiling questions. They can help you build a shower that both meets codes and will last while giving good service.
You are right to want the drain in the middle of the shower, it looks best and performs best while ensuring you don't end up with sever slopes to the floor.
Ensure you put your liner on a sloped floor, not flat on the floor, or the shower will accumulate moisture in the mudbed. While this technique is used (still), it doesn't meet the national codes and will end up with a swamp under the tile eventually, unless the shower is only used on occasion.
Important note - I'm not a pro
Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013