Between the numerous hangars, aircraft shops, welding shops, garages, etc., I have been in or worked in I have a good idea what I'd build for MY uses. But really folks have covered the essentials.
Right now I'm relegated to a 10x12 shed, and the 10x5 storage on the end of our half collapsing car port. I LOVE renting! ugh,...

Anyway, my list:
Good lighting, light interior colors on all surfaces.
Lots of outlets, 110 & 220.
Underfloor or overhead radiant heat, and for cooling a couple greenhouse fans on the walls.
Commercial grade epoxy coating on the floor
Storage loft w. overhead hoist
Outdoor enclosure for air compresor
A water closet w. shower
Reserved space with a couch, a TV, and a fridge full of my favorite frosty cold libations! grin

1956 GMC 370 dump " 'Tater "
1970 VW Volksrod "the Black Bomber"
2007 Chevy Avalanche
2020 Jeep Cherokee Trailhawk,
2005 Harley Davidson FLHTCUI

I dig all cars, old and new, whether they were hammered out of American iron, German steel, or Japanese tin cans. Being unable to appreciate them all is missing out on a world of great things.
But thats just MY opinion! :P