The shower pans come in different sizes and the drain holes are located in center and at ends. So the best thing to do is look at one you want and get the measurments for the drain and install the drain to fit. The top of P-Trap should be below concrete if yo can do it, if not get it as low as you can, make sure the pipe has pitch to it. Let me know if you need any more help.
Art retired plbg