At aprox. 1:45pm Danvers Fire Alarm dispatched a box alarm for a reported fire on the roof of the Town Hall Building at 1 Sylvan St, unoccupied, undergoing renovations. The fire was reportedly started by a working welding copper flashing, the fire appeared contained to the D side of the building in the roof area. Firefighters had a difficult time gaining access to the fire due to the construction and had to open up multiple areas both on the roof and inside the building, the fire was placed under control approximately 2 hours later. I arrived after the 3rd had been struck, just time to catch the last visible fire darkened down, and had to shoot through a forest of utility wires.