I built an outdoor shower. It uses a propane-fueled on-demand heater for making hot water and it connects to a garden hose.
It was designed to be quasi-portable, meaning that it can be taken apart, transported and reassembled at another location without too much fuss.
I'm in Northern California, so redwood is readily available. It is the wood of choice for using outdoors due to its resistance to rot. And it is beautiful.
I started by building a basic floor something like a standard wooden pallet. I sat this on the ground and put logs and boards underneath it to make it level. I didn't do any plumbing -- no floor drain or anything. The water just runs through the gaps between wood and soaks into the earth beneath the shower. It's mostly just going to be me using the shower, so there is no need for plumbing, in my opinion. If the shower were to be used regularly by several people, then it would be wise to have a floor drain or other means of directing the water away to avoid creating a bog pit. In this soil, one or two showers per day will soak in just fine.
Next, I added boards to the sides of the floor to serve as wall posts. One board at each of the four corners. I screwed them in so that the two sides would be easy to remove as intact panels then packed up and transported elsewhere.
Beams are added to make a nice structurally intact box. Important to make these level and square, but equally important not to fuss about things being overly level or square. Better to be true to life than to be perfect.
Next I added boards to serve as a place to mount the shower head and to attach the screen around the sides. I was referencing Japanese-style sliding doors. I used a woven poly shade fabric for the screen. It is heavily UV resistant and durable and water won't affect it.
I mounted the on-demand propane hot water heater unit on one of the sides. The shower temperature can be adjusted by walking naked outside the shower and toying with the knobs.
It's a richly satisfying way to bathe. I love this shower. It is exquisite to look up through the steamy water stream and see the tall redwood trees overhead. Forest bathing.