Maybe I’ve missed something but if there is no pipe or gutter then where is the water coming from?
Even though you seem quite sure that the leak into your apartment is due to defective concrete cancer work above you the water still needs to enter the floor or wall somewhere? Unless its condensation it just doesn’t appear from nowhere. Is there a bathroom above you? Maybe the issue is a leaking tap or kids splashing to much bath water on to the floor which is an owner responsibility. Or is it a rooftop garden? Did they waterproof above?