Nice side by side video on youtube of #1 and #3 explosion
http://www.youtube.com/watch?v=1Q3ljfLvHww"
Very impressive to see the difference in shape and power.
If you look at the frame by frame version of #3 explosion,
you can clearly see the fireball, followed by the implosion and...
From the picture you attached I think nothing from inside the building has damaged the roof. Something has landed on top of the roof. It hit not directly from overhead, more a bit from the side, so it bend over the wall.
If you take a closer look to the object it is partly above the roof...