I recently completed building a new black and white darkroom, intended for silver printing and alternative processes. I got an 8 foot sink instead of a 6 foot as in my old darkroom. I wish it could have been 10 feet, but there wasn't room. Still, it is nice to have so much more room for trays and beakers.
Another significant change was that I made it a sit-down darkroom. I found that I just can't stand for 8 hours at a stretch like I used to. In my new darkroom I can sit and think, relax, and plan new strategies for making images, whereas (thinking back on it) I was never really comfortable in my old darkroom.
Since I mix most of my own chemistry, I devoted a whole corner to chemical storage and a mixing area. Another corner was devoted to a print drying cabinet, with a filter and fan, and a UV exposure unit built onto the top of it. I painted the interior of the exposure unit bright white to reflect the UV around, and lightproofed the drying cabinet below so I can dry coated paper in it safely. I use the top of the UV unit for my densitometer. My countertop area is 4x8 feet. I could still use some more horizontal work area, but it is luxurious compared to my old space.
I have shelves and cabinets on both walls. The lowest shelf above the sink is a wire shelf, so I can use it to drain wet beakers, funnels, etc.
I have two enlargers--a Beseler 4x5 and a 6x7. I left enough space for an 8x10 enlarger, which I am in process of building, that I will have to roll out and project onto one wall.
I have 20 duplex plugs in the darkroom on two circuits, and if I had known in advance where I was going to have to place some of my equipment I would have installed a couple more at a different height. But so far 20 has been sufficient, though I have had to add a multiple outlet on the floor to accommodate a timer and light.
I built in two work lights that can be moved about for detailed work on bromoils or print spotting. I have a dedicated green safelight above the sink for examining negatives, and a reflector with 25 watt bulb for inspecting prints in the fix. I bought a bunch of safelights on e-Bay and have them all over the room--oh, I forgot to mention four additional duplex plugs on the ceiling on a separate circuit, wired to a wall switch, for the safelights.