Custom Shower Pan
Are you using a custom made cultured marble product, or a mud bed type tile base?
either way it doesn't sound like it should be a problem.
I recently installed a one peice custom CM base, with an offset drain to miss the framing, and the entry curb on the short side (a little non-standard, lol)
I plan to tackle the tile walls soon, and have been getting great advice from some of the pros here (look for the thread in the "remodeling" forum.)
I've seen many oddly shaped and sized tile showers that worked out fine.
Good luck, and let us know how it turns out.