I vote for the heated floor. One of my cousins did that (he builds commercial buildings for a living) and it is heavenly. Super easy to do while building, too.
When my wife told me she wanted to move back to New England from South Carolina (in retirement) I was less than thrilled. In fact, I hated the idea and she knew it but here we are watching the snow fall in Grafton, MA just the same. I found that being close to grandkids can be a big magnet.
One thing she offered to get me to be less hostile to the move was to build a 24' square, 2-car detached garage, mostly to house the Speedster and her car. I was constrained by underground septic in two directions, but 24' is OK if you put your shop on the same side as the Speedster - they both fit.
This one is a pre-fab job from a company in Connecticut and has 11 ft ceilings (we just made the foundation walls a bit higher), a full attic and 8' high doors. It was built off-site in parts and then assembled on-site in two days, including roof, siding and trim. Access to the attic is via a set of pull-down stairs in the center, so no floor space is lost to stairs. I think it's a 12/12 pitch so there is plenty of room upstairs to walk around (I'm 5'6" tall). The walls are 2" X 6" and it's fully insulated but not yet heated or cooled (although I can get it up to 70F in about 40 minutes using a Charboil "Big Easy" turkey frier)
OK, so things I would have done differently:
- Radiant heat in the floor slab
- A "Mini-Split" AC unit (you don't need the heat side, given #1, but it's handy if you keep the shop at 55F all the time and want to bump it up when needed)
- A Bend-Pak 4-post lift. If not that, then a 48" high scissors lift (I currently have the 3500 Quickjack for the Speedster but lust for something higher)
- Going to 26' square or even 24' X 30' would have been better for some larger machine tools, but I've found other tools in town to use, anyway.
- 220 volt 80 - 100 amp service (I opted for 110 only - bad forethought)
- Cat-5 Ethernet cable direct from the central house router
- Run high pressure air lines above the ceiling to the bench area and both bays
That's about it. Others will have more, I'm sure.