It's always interesting starting a large project on an uneven surface. The garage floor is sloped to accommodate quick water runoff with an appreciably significant rise over a 20' run. The area I chose has a net rise of 2½" over a 12' run, but it also has a level beveled edge where the floor and wall meet that I also had to take into account.
To get accurate measurements, I engineered a temporary tool which allowed me to assess level and plumb at the same time. I made this using a right angle protractor and a small level. This helped me verify that the measurements I was taking were valid in spite of the uneven work area.
Once I'd measured and cut the 2x4 to complement the floor's slope, I used the shelves to assure that my measurements would accommodate the space they required. I made a ½" tweak and marked the floor for later reference.
Then I got to work cutting up eighteen 8" horizontal support wedges from a length of 2x4. These wedges will be mounted to the wall to support the back corners of each shelf.
I drilled one pilot hole into each wedge and threaded a 2½" screw into it.
I spaced each wedge 36" apart horizontally and 15 & 3/8" vertically. Each wedge had Liquid Nail applied to its wall-mated surface and was then secured to the wall with the screw. Once secured, each wedge was individually checked for level, then collectively checked for level across the horizontal span. Once I was satisfied with each row, I moved up to the next level.
Having finished the installation of the horizontal wedges, I applied Liquid Nail to the underside of the slope-countering boards and placed weights on the wood to ensure adhesion to the (freshly cleaned) garage floor.
It's been a busy day and I got a lot done, so I took a few preliminary measurements on the vertical 2x4 supports and called it a day. Now it's time for pizza and a movie!