Figure out what service you'll need then double it. I agree with that, also have lots of outlets, and separate circuits. A shop sink with hot and cold runnung water is also a good idea, and have a first aid cabinet easy to reach. I would include some flush mounted threaded anchor points in the floor where you would be likely to want a flat table. You can put a coupling nut halfway on one of these anchors, and plug the top with a short bolt and washer, so you can embed it in the concrete flush with the floor surface. If you don't use them, they aren't in the way. Using these, you can adjust a framework to be absolutely flat, good for an assembly table, etc. Consider an area for a forge or heat treat oven, and build in suitable ventilation. In this regard, build in a floor level ventilation system for heavier than air solvents, etc, and maybe have a spray booth area, a clean room. You could use a heat exchanger in the vent system to minimize heat loss if that's potentially a problem.
Does it make any sense for you to have some kind of gantry from the ceiling to move heavy items around? That would influence your choice of roof structure.
Consider wiring in a loop of multi-conductor wire, useful for a number of systems. You may want to have an intercom system, and possibly a panic system. Some easy to reach buttons to alert someone in the house or wherever, in case of accident. Some lights in various spots to alert you to someone needing you.
If the air compressor is to be inside, build a room for it, to keep noise down. You might need a drain in that room.
A good humidity controlled cabinet for the myriad tooling that you want to keep rust-free.
You may find that the office should be large enough for a bit of a kitchenette. Handy to have a fridge and a microwave.
[This message has been edited by darryl (edited 09-29-2004).]
I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-