[chrismorse]

I second the idea of a single wide door rather than two. This might require deeper truss joists for a clear span - this will raise the building height a bit too.
Wider, for sure, space permitting.
A toilet for sure, unless your house is very close by.
A utility sink is great for many things.
Texas?? How about AC and insulation.
Bring in more electricity than you think you'll need, lights, refrigerator, (BEER), AC, welder, electric car charger, table saw?? the list goes on.
If you are going to have an air compressor, more electricity. perhaps build an insulated closet to keep the monster from driving you crazy.
When you design the slab, beef up the footing/rebar under the lift posts. (Use a lift with the hydraulics, cables and controls run through the top bar rather than on the floor, which is a pain to clean around, step over, drag tools over.....)
Less windows, more wallspace for cabinets/shelves/tool boards.
Might be worthwhile to have a sit down with your significant other to see what SHE might like to see out there: back up refrige/freezer, space for her hobbies and just possibly STORAGE.
Maybe do a She-Shed too :-)
Maybe make it a bit bigger, with an outside accessible door for mowers, yard equipment, bikes, that way they don't shed dirt and grass in Your space.
chris