corrugated steel plate; corrugated iron
Refers to a steel sheet formed into a wavy pattern for strength; used in construction and roofing.
The roof of this warehouse is made of corrugated steel plate.
トタン is galvanized sheet iron, often corrugated, but 波形鋼板 specifically emphasizes the corrugated shape and is a more technical term.
Compound of 波形 (corrugated, wavy) + 鋼板 (steel plate).