Place your pt plate & bolt it, do the layout, line up the studs with the top plates and snap a line across the drop, and cut the studs on your chopsaw.. you need to go up square & plumb for the roof & sheathing.

You can shim but I find it more work as you'll need to use strap ties with that large of a gap.

Next time you level the pad, and drop to the drain or door, usually with a water stop in the slab to stop water backing up into the garage. Then you won't need such heavy drop in only 24 feet.

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