Steve.
As usual, you're achieving a very convincing ground cover, ballasting and colour palette on Pontcwmyn. However, I'm not convinced that any full sized shed would have inspection pits going right up to or under the front face/doors of the shed. Even before current H&S laws (did the Factory Act apply to railway premises?), a safe walking route would be provided to ensure people didn't fall down the pits whilst moving around the shed and locos. I would expect a level path/roadway of 15 to 20 feet wide across the front of the shed. I'm happy to be proved wrong about this.
Dave.