Can the 14 ft. SM-Rib Galvalume Steel 29-Gauge Roof/Siding Panel be placed over a slatted patio cover to keep out rain and sun?

You would need substrate and felt.

To meet manufacturing recommendations, you would need substrate and felt. The 14 ft. SM-Rib Galvalume Steel 29-Gauge Roof/Siding Panels are not structural and would need support underneath them.