From DNA Info:
A 2009 [City Hall] renovation plan called for repairs to the roof and new safety systems, including a sprinkler system and improvements to the fire alarm. To increase electrical capacity, the city planned to excavate a new sub-cellar to house new equipment.
They also decided to fix the ceiling in the City Council Chamber.
The estimated cost of the project: $65 million.
As the work got underway, problems mounted. Workers installing sprinklers in the "bullpen," where the mayor and close staffers work, discovered "alarming" water damage to the roof tresses that required steel reinforcement.
The new discoveries and others sent costs soaring to a whopping $119 million — nearly twice the original budget.