Given the complexity of building a 32-story prefab tower—with taller ones to come—a number of building professionals were suspicious the firm could achieve the 20 percent cost savings Forest City has been boasting about. Among them is Jerilyn Perine, the executive director of the Citizens Planning & Housing Council and a former housing commissioner in both the Giuliani and Bloomberg administrations, where she worked on a number of low-income modular projects. “I’m not against modular. I think it has its place,” she said. “I don’t think it’s like discovering fire.”