I don't have any photographs of my darkroom (yet) but, I do have an Autocad image! Maybe I'm a computer geek but it's been very helpful to render and design the cabinetry/layout before I build anything.
The room itself is only 1.8m x 3m and I have to share it with two hot water tanks (not shown, at the end opposite the door). The red box in the foreground is a cabinet for my Omega D enlarger. It's a bit short since our ceilings are only 7 feet (you can tell I'm a Canadian because of the mixed units of measure). Still , I don't have enough clearance to raise the head all the way.
My wet counter is sloped at 2 degrees into a big porcelain farmhouse sink. I have a dry counter along the opposite wall (both not shown). The oblong red object under the wet counter is the cats' litter box. I don't recommend one of these in any darkroom but, I've gotta share.
I enjoy seeing pictures of all your darkrooms but I'd love to hear what your favorite feature is. If your friend was builiding a darkroom, what would your one recommendation be? Mine would be my sloped wet counter, it puts the trays at a nice height and any spills just flow downhill.