Choose a corner to start with, and mount a light with its center about 6 feet from the nearest short (40-foot) wall and 80 inches from the nearest long (60-foot) wall, with the long side of the light parallel to the short wall. Since each shop light will cover an area of 160 square feet, you'll mount your first light so that it is directly in the center of the first such area in the corner of your shop.
Mount three lights evenly spaced along the short wall. The easiest way to do this is to measure for the placement of the light in the other corner of the same short wall, as above, and then place the middle light directly in between them in a straight line with the other two.
Measure for the next row of three lights to start 12 feet from the first row along the same long wall and repeat steps 2 and 3. Repeat this process 3 more times, until you have five rows of three lights. Pay special attention to the last row next to the second short wall to make sure its placement mirrors the first row you mounted in step 1.