I've been mired in a long-term, down-to-the-studs remodel of the house I'm living in. This made it necessary for me to make a 'temporary shower,' which I move about as I work on different areas. This shower has taught me a few things about shower design, details I will incorporate in the final, permanent shower.
The first is the question of size. I used the largest pre-made pan I could find- it's about 36" x 48". Amazing! I have the most comfortable shower I've ever had - no banging my elbows into the walls from it being too small, or 'cold spots' from it being too large.
I added a taller threshold- an angled board ranging from 12" to 9" over the length of the shower. This prevents the shower curtain from leaving the shower area, yet is low enough to not get in your way. (I had started with 12" across, but my foot kept hitting it).
I've learned that the shower head is best placed at the corner near the entry- rather than in the middle of the wall, as is common.
I've learned the need for a place to rest a foot, about 9" off the floor, on the side farthest from the shower head.
The shower valve is best placed between shoulder and face level - somewhat higher than is usual. The shower head need not be much higher than you are tall.
A length of ordinary rain gutter, placed at about 60" on the 'far' end, has worked quite well as a place to put your shampoo, etc.
Here's the real surprise: I've learned to appreciate WINDOWS! In the original location, I had to add small shoulder-level windows so I could operate real house windows that were behind the temporary shower. These were located on the 'far' end and on the back wall, about a foot from the far corner.
I found it to be quite nice to be able to look at a downward angle into my back yard. It sounds silly, but taking a shower is a lot nicer when you can see the new flowers on the tree, or the squirrel out collecting nuts. Even IF someone were to look in, the most they could see was my head. Located where they are, they receive almost no over-spray or splashing from using the shower..
As I move the shower about, I continue to enjoy a 'view' from the shower. Even when all I can see is the water heater a few feet away, having that window opening really takes away from the 'closed-in' feeling a shower can have.
These windows are simple openings - unlike a glass door, you're actually looking out of the shower - and not at a milky white panel.
Since I have this shower on a platform, I added a stout handhold at the entry, at about shoulder level. I find it's presence quite reassuring- even though I don't "really" need it to exit the shower (platform is even with the floor of the shower).
Being portable, there is -of necessity- a gap between the top of the shower and the ceiling of the house. This gap is about a foot wide. Again, there has neen NO overspray exiting the shower here; nor have I noticed any sort of draft. Yet, the shower benefits from lots of ventilation - no mustiness here! I had run a 'shelf' across the back to serve as a brace (this is about 6" wide and 72" above the shower pan) .... only to find the cat loves to perch there as I shower. It seems the best drinking water drips from the shower head :D
As for materials .... I have been delighted with how FRP has worked out for me. It has performed far better than the usual tile, lacking grout lines to collect crud. Lexel has, by far, proven to be the best caulk- especially for my drain opening. What wood is exposed to moisture has been well protected by simple shellac. The platform itself has been well protected by "spar" polyurethane; I had sprinkled some silica (white) sand on the wet poly, and that continues to give me a non-slip surface.