5x7 - lots of room for a wet darkroom, but beware of its dark side..
Mine is not much bigger than that - the door is in the middle of the 7' side, a pocket door.
The wet side is a home made fibreglass over plywood sink about 22" deep by almost 5' long. There is a shelf under half the sink for gallon jugs, drying screens on racks for prints on the other half. A vertical print washer sits at one end of the sink.There are a bunch of shelves over the sink on adjustable brackets and rails for larger dry chems bottles, and quart sotock solution storage. Opposite the door is a small cabinet that has a low counter where the heater cooler sits. Above this is a not to deep cabinet for dry chemistry, and small bottles of stock solutions.
The dry side is a 30" deep plywood counter that the enlarger sits in the middle of. Behind it up high are shelves, again on rails, for books, manual, binders of negatives, slide carusel, etc. Below the counter are 36" deep surplus deep drawer units, and in the middle are a pair of 12" deep units.
Storage galore. Put doors over as many 'little things' storage locations - it is so much easier than vaccuuming all of them.
Read up on ventilation threads. I have contributed to a few It becames increasingly important with color work, where everything is usally warmer, and therefore evaporates that much faster. Plus the chems are a wee bit less nice.
For big stuff - 20x24 etc, I put a big long plywood sheet over my carefully levelled washer and dryer in the adjacent launry room, and use the laundry sink as my water source and drain in those cases. I work from one tray at those sizes. I usally have to deal with any laundry back up while I have commandeered the laundry room in these cases.
I also use my darkroom to wash out, ferment and bottle home made wine, and when making home made soaps - try that in your sales pitch if your significant other is showing resistance to the idea of a darkroom construction budget.
Get a list made of all the things you need to do to the house before you start your darkroom. Set a cash and time budget to get at least 3/4 of the big (ie a weekend or more effort is required) items done; I suggest not longer than 1.5 years. Then start the darkroom. the other 1/4 of the original list will never get done, or will take 5 years to get accomplished once you get the darkroom going.
Negotiate a darkroom night a week, to start, and stick to it. That way your partner will not kill you right off when you get home from work, wolf down dinner, disapear into the darkroom, and never speak to them until they shake you awake the next day because you were focussed on perfecting that print and crawled to bed at 2am.
You can spot prints, select prints from a contact sheet, cut a matte, or mount a film in filing sleeves here and there; maybe even process a film before that night to get ready, but try not to print more than 1 night a week to start; break that rule and you can tread down a road that will test even the most loving relationship.
Once the initial flush is off, and you have used your new wet facility for a few months the maniac phase will have faded, and you will know your limits and be able to monitor your behaviour better. Photography is a great hobby, but a wet darkroom is usually a solitary pursuit.
Happy planning for your new facility.
