When I think of a man cave, it’s a place where a woman wouldn’t even want to go, so less a gaming/TV room (which I also want) and more a car/workshop/weight room. I only have one bay available now, where I have a squat rack and fridge, with enough room left over for my car when I need to work on it. My plans for a 3-car garage include one bay for storage, tools, workbench, fridge, sink, and small bar, another for a lift (the weekend car stored above the daily driver), and the middle bay for a couch, end tables, lamps, squat rack, and folding treadmill. A moderately-sized (42″?) flat screen would hang somewhere, maybe a neon beer sign or two, and it’s almost a requirement to have at least one barely dressed girl poster or calendar. Wifey thinks that’s incredibly tacky, which only pushes me to do it 🙂
Ideally it would be fully finished, insulated, and vented for HVAC. If money wasn’t an object, I might build in a tiny half-bath, too.
My advice is to not skimp by getting a mini-fridge, as I did. Go nearly full size – it’s hugely useful for parties.