All of the following roofing materials may be installed over open or "skip" sheathing EXCEPT

Wood shingles can be installed over open or "skip" sheathing because they are designed to allow water to drain and air to circulate. This system helps in reducing moisture buildup and potential rot, making wood shingles a compatible option for such sheathing.

Similar to wood shingles, cedar shakes or shingles can be installed over open or "skip" sheathing. They also benefit from the ventilation provided by this type of sheathing, which helps maintain the integrity of the wood and allows for adequate moisture management.

Terra cotta or concrete tiles can be installed over open or "skip" sheathing, provided that appropriate underlayment and battens are used to support the tiles. These materials are heavy and require secure anchoring, but they can still function adequately with proper installation techniques over skip sheathing.