The invention concerns an assembly of roof battens which enables them to be stored in an assembled state and layed rapidly at the desired spacing on a receiving surface such as the rafters of a roof; a continuous flexible sheet is held in place by stapling strips onto the battens where they intersect with them, in such a way that, after the assembly of battens has been layed on the rafters, the continuous flexible sheet forms a deep central trough between two adjacent rafters to allow water to run off.