I'm planning to remove a bathtub and replace it with a shower. I'm planning to create the shower base myself, rather than buy a pre-made pan. However, I won't be able to move the drain, since I'm on a slab. So the new shower base will be the same dimensions as the tub, with the drain in the same location. Is there any problem with setting up the shower this way? If I put the shower drain on the end rather than in the middle, will it lead to any issues that I'm not expecting?
As long as you have sufficient slope to the drain you are okay. Typically 1/4" per foot.
the only thing stopping you is wether or not it is a 2 inch drain. almost ever 1 tub to shower convertion ive done has been 1 1/2 inch drains. shower need that 2in. drain to be effective. with 1 1/2 in. the water could fill the base. other then that, drain placement make no difference for a custom pan. 1/4in. per foot off the longest run, transfer that line around the rest of the base. and if your doing a 3 piece shower drain please remember the preslope.