It can save time and effort if the installers attach the L-feet at Ground Level, rather than on the roof.
Start by placing a box of 4 panels on a flat surface, remove the straps, place the cardboard lid down as your work surface, and place the first panel face down on the cardboard box lid. Next, visualize the panel pair placement so you can attach the L-foot and U-foot to match the position on the roof, considering Left and Right pairs, plus upper and lower panels. Tighten firmly, and allow a Clockwise final twist to square it up. All 4 panels can have the L-foot attached in under 10 minutes, ready for hoisting by a rope up the ladder to the roof.