It might not be arson. The Kingdumb Hells are known for sloppy workmanship. You have window washers building the damn things, and they have to go up in three days. They use crap materials to save money, and people do not always know what they are doing when installing the electric and gas connections.
This might have resulted in a number of potential fire hazards. Short circuits and wires with too much current lead to fires, especially if those clowns don't know how to wire up the fuse box so it will do its job. Short circuits are not surprising, given that window washers are hooking up the outlets. Heaters are also hazardous when poorly installed or are of crap quality. They could have a gas leak or flammable materials where they could ignite. These things can blow up or catch fires.
If the fire was near the roof, my best guess is that the lighting is at fault. All it takes is for those window washers to mess up when hooking up the light fixtures, and you get yourself a short circuit. Not to mention if they dubbed up on the roof, it leaked, and water leaked onto live electrical lines near the roof. The exterior lighting is the most likely culprit. And, with the crappy materials and wretched labor, I am surprised that more of these ugly structures don't burn to the ground.