Loading heavy 4×8 plywood sheets on top of a car is a challenging task when there’s no helper available.  I developed this system of side rails that hook onto the ends of a bar-style roof rack.  Avoids damage to me, the car, and the plywood.
I started by adding a horizontal piece to the car’s roof rack.  This extends out sideways, extending about a foot from the side of the roof.  A short piece of dowel is added to each end of the horizontal piece, and the end is rounded off to permit the plywood to pivot more easily.
When loading and unloading, the 2×4 side rails hook onto the ends of the horizontal bars.  The hooks are reinforced with plywood splines for strength.  “Steps” of short pieces of 2×4 are added to the rails.  The lower step provides ground clearance for the panel carrier used when moving the panel.  The upper step provides an intermediate resting place when lifting up the plywood.  Video here:  https://youtu.be/FNlRBYYbkWU

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