1/8-inch in 10 ft is actually reeeeeally flat. Doesn't help the OP much, but the ACI 117 commentary describes a 1/8" in 10 ft as "superflat", corresponding to a FF50 floor flatness when tested using the F-number system that is much more commonly used in commercial construction, at least in my...
Re: Designing detached garage - looking for input
Even if you don't think you'll need it, I'd still think hard about water/drainage, or even just running below grade piping and a hose bib now to the outside garage wall and bringing in overhead PEX later if needed. Run under slab drain piping...
I'd heavily recommend using chairs for holding steel reinforcement in the slab - and I'd use rebar, not welded wire fabric.
Do you have a tornado shelter? There are drop-in prefabricated units that you could add later; designate a spot for one now and add grade beams/rebar around the future...
I'm looking at Wall Control metal pegboard panels for a garage workbench project - expensive (about 5-10x the price of 3/16" hardboard pegboard on a $/sq ft basis) but excellent reputation. Stuart at toolguyd.com loves 'em. You have the option of using 1/4" heavy-duty hooks, or the special Wall...