For the tall unit, use the bottom wall plate for the bottom of your box. Attach the plywood to create a 1-in. gap at the bottom for removing dirt or dropped items. For the shorter slant boxes, install your own blocking to create the bottom; leave a gap at the bottom of the plywood for those, too. We show 48-in. and 16-in. versions; you can make yours any depth or length you want.
Note: If your garage has a short ceiling (or your tools have extra-long handles), create a cutout in the top of the plywood face, as shown in Figure A, to allow more entrance and exit leeway for your tools.