Generally, I like the design of this wash stall. I might have a larger drainage grate along the wall and, since there appears to be another wash stall on the other side, raise the partition about 6 inches to let the water from both sides flow into the drain without eventually damaging the wood. Also, I'd include a spray boom to keep the hose out of the way.
Tipping House Estate has an archway that divides the main estate from the cobbled stable courtyard. The present from the past.... The stables are older at Tippermere, and their's a fountain in the centre of the yard, but the archway is something like this. Stone stable and courtyard