Larry for the interior you have about two choices, ceramic tile or fiber glass enclosure.
Now, the exterior is just a piece of cake, build around the enclosure either having a door or one of those walls like in state parks. I would use the masonite sheets for the exterior with 1 x 4 corners and picture framing. I would build a hip roof system allowing for nice wide soffets for rain sheding. Gutters not needed.
Will be a fun project and not to difficult at all. You might even want to have fun with those glass blocks to make a window for light. All kinds of possibilities.