What a great question.
Flooring: something easy to clean, where you can see and easily retrieve dropped objects. Definitely not carpet. I prefer wood, but tile or linoleum work. Concrete floors are just too hard to stand on a lot.
Lots of electrical outlets. Maybe even a couple on the ceilling, especially if you have a long arm or are able to have an ore industrial sized steam iron.
Lots of compact storage areas.
I prefer a cutting island, where I can go around to cut without moving the fabric. The a larger area for laying out the quilts.
I'll let others add about lighting.