Abstract: The present invention provides a ceiling drainage system for decks, canopies and other applications acting under a similar operational environment. The system is designed to attach to the underside of a conventional structural framework such as an outdoor house deck or a stand-alone canopy. The system provides a watertight snap-together ceiling that keeps the underneath area dry as to create outdoor living or storage space. The multi-paneled ceiling system is unique with its all-plastic construction and its multi-functional watertight snap-fitting interlock feature. This snap-feature maintains a watertight joint between adjacent components while allowing for thermal expansions and contractions of the modular plastic componentry and the inherent movements of the supporting structural framework. This system given its simplicity provides a superior “do-it-yourself” installation procedure for the unskilled homeowner or builder.