I built a darkroom in a half bathroom in an apartment I lived in, after I finished school. The main bath was off the ensuite, so the impeding of use of this bathroom's primary functionality during darkroom operations was not an issue.
It was about 3' wide by 6' long. The enlarger went onto a strong narrow shelf that I anchored to the rear wall, above the toilet, and braced the top column with wires and turnbuckles to line it up. (Enlarger was a Beselar 23C)
The removable baseboard shelf sat on rails attached to the walls, about 3' apart that were on either side of the toilet. This shelf sat level with the fixed enlarger shelf.
Below the top shelf were two removable shelves that also sat on rails anchored to the wall. The top shelf held the developer and stop bath tray, and the lower shelf the fixer and wash tray. The print tray syphon overflowed into a 5 gallon pail that would periodically be dumped into the sink.
Print processing was done while seated on a low stool.
The setup was less then ideal, but all that I could fit into this space.
The best bathroom darkroom gig I saw where there was more room was a pal from school, who put his enlarger on a second hand microwave shelf (back in the 80's, before a microwave spot was standard equipment in a kitchen). The cabinet under the enlarger stored the chemistry and suppies so they could remain as dust free as possible. He could wheel it from his room to the old victorian bathroom (actually once a bedroom with plumbing added a few decades later). An upside down funnel over the tub drain, and a hand shower thing attached over the tub spout made a great print washer.
We had built a fold up plywood affair trimmed to snug to the tub top contours that sat over the bathtub to present a counter height support, and then had a surplus from old kitchen reno counter top we hauled home on trash day as a work surface. When not in use they stood folded up on end behind the bathroom door.
For safelight (he only only printed at night) the window was covered with multiple layers of red tissue paper. Film was loaded onto reels in a changing bag. Prints dried on a retractable clothes line.