Hello, from what I deduce is a flat roof ... the ceilings being so, have that problem, so you MUST make a roof cover, or LOAD, for what? 1st- Create a slope necessary enough, to spit out the water and do not stagnate. This slope has to be 1.5 cm to 5 cm per linear meter ... (the closer to the 5 cm you are the better) that will be done according to whether that terrace is accessible passable or not. 2nd- this cover protects the crockery from weather inclemencies, the slab dilates and contracts like all materials, producing cracks, if the expansion joints were not made ... 3rd - the roof works as a thermal insulator, the roof is the surface of the house that has the most sunlight in summer, therefore it causes great energy consumption .... to cool the interior. We go to the solution ... the most advisable thing is to make a series of layers on the slab that will avoid long-term problems ... CHEAP IS PAID TWO TIMES and the second is always more expensive. the layers are: Barrier cuts steam: this barrier allows water vapor to condense, leaving it on the outside of the house, this barrier is simply ASPHALT PAINT, YOU MUST COVER ALL the roof surface with at least two hands, one hand from north to south, and the other from east to west. Lifting mortar: with this mortar you generate the slope towards the chosen place to evacuate the water, gutters, drainage mouths, etc. This mortar is made with a dosage 1 / 2-1-3-6 (half bucket of cement, 1 of lime, 3 of sand and 6 of ground telgopor, pearls of telgopor or pearls of telgopor, as they call it) you can do it too with 1-3-6 (one of cement, 3 of sand 6 of telgopor). Once this mortar has set you can opt for two paths. PERFORM WATERPROOFING. (You can use liquid membranes, ELASTOMERICAS or non-fibrated POLYURETHANICS or asphalt membrane) and also make a leveling folder, this fulfills the function of protecting the water-repellent membrane, prolonging its useful life for many years ... Or make the folder, and on top of it make the waterproofing ... and make some thermal insulation on top. THAT'S THE MOST HEALTHY FOR HOUSING TECHNICALLY SPEAKING. they are solutions that take away long-term problems ... If you choose what you propose ... I suggest before, paint with asphalt paint, make the folder you decide, add water repellent (it is optional, because the sun will hit you hard the same there) and monele welded mesh, which will prevent it from dilating both the folder and cracking. then to the folder make a waterproofing ... with liquid membrane ... at least 4 hands ... (the more hands better) and every two years reinforce again with more membrane! Cheers