Not much to add. A friend has a nice outdoor one here - the best part is the big tarps overhead for shade. Those tarps that you see under tension made to provide shade - not the triangular ones, the square ones. Really nice here in FL. I imagine it would be nice to be out fo the drizzle in Oregon, too.
The feature I love the most about our wash rack is the overhead swivel hose. It’s so nice not have to drag the hose all over the creation. The next one is the sink with stainless steel sheet counter top. It’s gray water so you can just direct the water directly to the surface ground. I personally don’t like mat with drainage holes. My horses always give a big dump the moment I turn on the water. Imagine the frustration trying to scoop poop out of the holey mats… I use solid mat designed to be used in wash bay.
I love these 5 year old reappearing post mysteries!
Cross ties for sure (versus one tie ring), metal pole fencing/sides (no worry about rot or a horse doing any sort of damage to them), and 3 sides. I do like the idea of the gap in the third side so you can walk straight through. Either concrete higher up so that there is natural drainage away from the area, or gravel that is built for drainage. There is a show facility around here with gravel wash racks that drain VERY nicely, probably better than most concrete wash racks.