The scope. Receiving, staging, rigging and setting prefabricated roof modules, and the carpentry to complete the roof once the modules were in position.
Staging is half the job. On a constrained inner-city site there is nowhere to put modules while you wait. Delivery sequence has to match install sequence exactly, because a module in the wrong place at the wrong time blocks the crane from reaching the next one.
Prefab still needs carpenters. Modules arrive built, but they do not arrive joined. The junctions, flashings, tie-downs and completion carpentry between modules are what turns a set of boxes into a building.