There is provided a transparent plastic film roof for a building, comprising two transparent plastic films, which are fixed to edge rafters extending from a ridgepole to a ridge plate and are formed in a bag-like structure for serving as a building roof, wherein warm air is supplied from an air supply port into the bag-like structure to maintain the bag-like structure in a tensioned state, and air in the bag-like structure is discharged from an air discharge port. There is also provided a multi-ridge building, wherein a liquid passing pipe is disposed in the same direction as long film-clamping assemblies in the vicinity of a valley portion of the multi-span roof formed by the two transparent plastic films, and wherein the liquid passing pipe is configured to pass warm water or warm antifreezing fluid therethrough.