Off the top of my head, I'd think of using a 4x4 post for an upright, with pipe straps to attach a 1/2 inch PVC pipe along it. Maybe a valve halfway up for control. Elbow off the top to a short arm to hold a shower head. Elbow at the bottom to a garden hose thread female connector.
Yes we did - It is a 2" PVC pipe with a garden shower wand attached - The wand turns to the side to be in the "OFF" position and straight on towards the shower platform to be in the "SHOWER" position. The wand is secured by set screws and a hose clamp. We used the textured Kryo Paint made for plastic to paint the PVC a nice hunter green to match our decor. The wand has a short 48" hose section attached to it up inside the PVC pipe and it is then connected to the longer hose or easily disconnected when we need to move the hoses or something - (the reason we didn't just connect to a longer hose to start with) The platform is a cedar deck boards and pavers, with pavers going to the steps of the pool - the shower is tucked into a cul de sac of the trees for a bit of wind protection and privacy from the rest of the yard. The sun on the hose almost always heats the water up enough to have a decent short shower before and after being in the pool - it probably cost under $20 for the shower and the platform and pavers were extra but a nice touch.
Harkening back to my days at the Boy Scout camp... We rigged up the showers with a drinking fountain handle - spring loaded, normally off. That was overhead, with a pull string coming down. Then an elbow and a cheap showerhead. Nobody gets to just stand and soak and create a huge mudhole, they hold down to get wet, let go to lather up, hold again to rinse. Like the showers in M*A*S*H.
Well I'm guessing for a few bucks you can purchase the Solar Shower thing from Cabelas or the camp store, maybe even Walmart too. We had one for horse camping until my DH kindly bought me a "Hot Water Now" unit - anyway, the Solar Shower unit holds about 4 gals of water so that may be something to think of too if you don't want to put too much work into it - they even sell a fabric "cabana" that hangs up around it....
At our cabin, in Ky, when I was growing up, we had the coldest well water on earth. Our shower building had a big, galvanized, stock tank on the roof that warmed the water enough to even get warm on summer days.
I have several of the camping shower bags. The main problem with them is if the sun is searing you can almost scald yourself.
I saw a picture of one online that looked interesting recently made out of PVC, it was built to be connected to a standard garden hose. Basically it was a large diameter (4 inch or so) section of vertical PVC pipe painted black with a T fitting and reducer at the base and place to screw in the garden hose. The top of the large diameter pipe had another reducer on it with a 90 degree iron pipe fitting probably 1/2 or 3/4 inch, then a short 5 or 6 inch section of pipe, a lever valve with a return spring and a pull cord on it, then another couple of feet of pipe, another 90 and a shower head. My guess is the large section pipe acted as a solar powered water heater.