Most concrete roofs follow a similar type of construction.
Concrete slab roof leaking.
However concrete is porous.
This cement layer is known as a screed and contrary to popular belief its purpose is not to waterproof the roof.
You have a rock hard concrete floor and it seems impervious to water intrusion.
Do waterproof your roof.
It must be under slope.
Most likely you have just a concrete slab and not roof system with layers of insulation what you should do is to cover concrete with metal sheet for example.
Concrete cannot be the top layer of any roof.
A 10 to 15 cm thick slab of reinforced concrete with a thin 2 to 5 cm thick layer of cement on the top.
Here in florida most building foundations are concrete slab.
Concrete also cracks and those cracks will be the first.
The most common complaint with regard to both concrete tile and flat concrete roofing is water leaks.
Roof penetrations are found on many flat concrete slab roofs.
No water isn t going to soak up like a sponge but concrete does allow water to seep through when there is enough.
What is extremely important is that this metal sheet isn t horizontal.