As mentioned above, add LOTS of outlets and lighting. If you are welding or heating, make sure your service will handle as much 220 as you need. If you have a compressor add plumbing so you can locate drops throughout the shop. Insulate and put plywood on the lower walls. A bathroom is a VERY nice upgrade. Definitely add the lean-to's - there is no such thing as a shop that's too big. Being able to get stuff out of the weather is a godsend. A pure luxury I added this year was a mini-split so I have heat and A/C in my shop. It's almost indecent how nice that is. Good luck, and post lots of pictures!