As you probably know, most roofs in Pakistan are flat. This makes them easily susceptible to leaking.
This very informative video shows roof construction of a typical Pakistani roof. Concrete is being mixed and poured over the roof, which is the final step after the base of the roof has been constructed of other materials.
The base of Christ Public School’s roof is constructed of steel girders and bricks. Then the concrete “mason work” goes over that base.
You can see photos of the existing base being constructed in this post from October 2013. But now the rain is already leaking through that roof, built a little less than 3 years ago.