You don't want those angles in the drain, you'd never be able to clean it if it needed it and the trap should be directly below, not offset. To keep the required slope so it would drain properly, it could raise your height too far to install the drain assembly. Probably not a problem over 6", but it would depend.
Are you planning on tiling the walls? If so, check out www.johnbridge.com. While there are some decent pre-made shower pans, it isn't really all that hard to make a custom, traditional one. You must pay attention to detail, but the actual work is pretty straighforward. There are some other techniques that work well, too: Wedi and Kerdi come to mind. With Kerdi, you can make a custom mudbed and then do the waterproofing if you cannot use their pre-made forms. Wedi parts can be cut, and one might fit what you want to do. Kerdi is easier to find, but Wedi is available if you look.