Cement Slab as roof for elevation

We have constructed house through contractor and for top floor staircase its open to sky and their is elevation wall built on four sides 7 feet height and its 4 inch thick wall. 

Now to cover the roof contractor has put 2.5 inch concrete slabs of 2 feet width and 7.5 length and in that 1 feet will be projected outside and total he used 6 no's 

They are poured on ground using the steel reinforcement of 12mm rods and 8 mm rods.

 12 MM 5 No's and 8 MM for every 5 inch and poured concrete and the total thickness of that slabs is 2.5 inch and after 7 days he lifted and placed them on the walls.

Now my doubt is will the wall hold that weight and not collapse after some time. As per him he says it will safely hold as their wont be any other weight as we are not going to climb it. Not sure, but  i am getting paranoid when ever i look at that elevation roof.

Please help me whether its correct that 4 inch walls on four sides will hold the weight and not give up after sometime and break the entire elevation.

Regards

Neel