Is the 12 ft. SM-Rib Galvalume Steel 29-Gauge Roof/Siding Panel strong enough to walk on?

No.

No, the 12 ft. SM-Rib Galvalume Steel 29-Gauge Roof/Siding Panels are non-structural and would need substrate installed underneath to support the panels. Our recommended minimum substrates are 15/32 plywood or 7/16 OSB decking.