I live in S Dakota and had a friend build and outdoor shower in the Black Hills on his place. He just used cedar boards, I really can't remember if they were treated or not. He was 6'6 so he made it 7 feet tall and was about 4' square. He put a drain hole in the floor boards to offer easy drainage that would run down his hill. No one could see into it unless there was a place higher up the hill! It worked great and was nice to use!