I built 8' walls on a 2' concrete perimeter foundation. Subtract 6" for the concrete slab and that leaves me 9-1/2' of headroom in my garage shop. I can stand 8' lumber vertically, and even flip plywood sheets diagonally without hitting the ceiling. For the rare times I have longer boards, I simply store them horizontally, or cut into shorter lengths.

8' walls were cheaper to build, easier to insulate, and I didn't have to install fireblocking or other reinforcing in the framing. And the lower ceilings make the space easier to heat.

One possibility if you need to stand longer lumber vertically, is to keep a lower ceiling in most of the shop, with a raised opening where tall lumber can extend up into the attic space. That would keep your construction and heating costs down, while providing tall vertical storage.

Anthony