Depends. Generally going "up" is not that more expensive (with some limits) as it's largely the same labor and same foundation.
One thing that gives shops a lot of flexibility is door size. A 14' eve generally allows a 12' door.. That's great for most things, but if someone ever wants that shop for RV storage or big boat storage, you may want to consider a 14' door (16' eve). This clears anything that can drive on the road (or be towed on the road).
I have a 16' eve on my shop. My pitch is relatively low. There are parts where I'd like to put a mezzanine, but once you consider that the framing of the floor probably takes up 12" or so, you end up with pretty low ceilings at the eve... If was doing it again, I'd probably move to an 18' eve if I wanted 2 floors internally.