I have one, about 500sf. Started it modestly for my wife's daily morning routines, with adequate gear for me to get in a lift if I couldn't make it to the gym some days. Working at home, I used it as my getaway.
With COVID I had no choice but to expand, and thankfully I'd added a few things slowly before it hit so I snagged some good deals.
I have no pics but let me see if I can rattle off what we've amassed now:
full cage w/multigrip pullup
pulley setups
600lbs of plates
wheeled plate tree
Bowflex 1090s (want to swap these for 552s and get pro style 60s-120s eventually, but not at these scalper prices)
an assortment of smaller DBs, kettlebells, bands, weighted balls, steps, plyo boxes, vests, wheels, etc.
landmine setup w/grip & squat attachments for all sorts of stuff
leg extension/hamstring curl machines
full pulldown/row pulley machine
seated calf
sissy bench
FID bench
full commercial adjustable bench
a wall of pulley accessories
heavy bag
elliptical/bike
Olympic rings, adjustable dip bars so I can go WIDE as hell for bodybuilding purposes unlike most available setups allow (this is huge for me, few seem to ever care or consider it)
and of course, full length mirrors, flooring, and TV w/surround setup throughout
I think that's it. I always want to expand but I also want to not be a spendthrift. Otherwise I'd outfit the entire basement with top notch stuff all at once, but I have no need. All I really need is a barbell and a rack and I'll be fine, but working out so much at home with limited equipment got old FAST. The gym has its merits for sure, even though I still stuck to the staple stuff when I went. There are a couple things I'd like to get but when I can just hammer away more with freeweight work as an alternative, I find it hard to justify certain equipment at $1000+. I DO want to get either a cable crossover or dual wall pulley stacks for a multitude of uses, that'll probably be next. Would also like to fab up my own dip station to my preferred specs, a la Vince Gironda