A roof or other cladding sheet (3) that is adapted to engage a concealed fixing retaining clip (29) is disclosed. At least one rib (65) or side edge formation (11, 31) of the cladding sheet has a lengthwise extending channel (61) that opens upwardly relative to a base plane of the cladding sheet and is adapted to receive retaining members 9 of the concealed fixing retaining clip. A roll forming method and a roll former are also disclosed.
