Abstract: A protection layer upon a building roof is constructed with hollow ceramic blocks which after laying constitute a water pool with desirable depth and an air space thereupon to provide insulation against temperature and weather abuse when the roof is otherwise exposed directly under rain or shine. A typical block has generally rectangular hollow cross section to facilitate free channelling of water and air. Openings are provided on top of each block for the intake of water from overhead, and drain openings are optionally provided in the bottom of selected blocks to communicate with the down-pour drainage of the roof. The height of the overflow pipe is adjustable to set a desirable level of water reserved in the pool.