I used a complete 3'x4' one piece shower. I trimmed the top to match the roofline where it sits. Across from it will be the toilet and sink in another enclosure built probably from interior doors. It will also be 3'x4'. Don't think that it was an easy install by any means. I measured several times before cutting and was told by most that it was not going to fit. Determination and ignorance has served me well.
Here's a pic from my thread: