Member - HaroldB has a beautiful screen door he made for his Casita. Search for "Two More Oak Wood Projects, Screen door and utensil drawer" and you'll see the amazing photos.
is a 17' so exterior door and screen door
are flat. I have not see a 16' in real life, but understand the door is contoured the same as the shell. Gord100's wooden door mentioned above looks like it would be easier to build than the one I did, since it is not connected to the exterior door. It looks to me it operates totally separate from the exterior door. I've built several screen doors for houses and none of them have been the challenge that the Casita
one turned out to be.