Now that the kids are on their own, well two out of three, I have the entire lower level of my house to myself , and there was alway a one bedroom, one bath in-law apartment downstairs too, so plenty of room.
The downstairs living room houses the band gear, and is great to practice in as it has a fireplace for winter, and attaches to screened-in porch, which is nice when it is warmer outside. I have a small tool room/shop, and the aforementioned in-law apartment.
Added bonus, my wife never complains about noise, so my band room gets used by everyone.
It is amazing how much time you have to fix/renovate things, (Read-Fixing up the man-cave.) and how much less cleaning one has to do when the kids move out.