Space on the penthouse level of Carriage City Plaza — once held out for custom-designed luxury condos during the housing boom — could feature another 20 units and other amenities for the massive downtown complex.

When the 16-story building was constructed just as the housing boom reached its apex, the penthouse level was never completed, essentially a blank canvas with the idea of offering 13 custom, luxury two- and three-bedroom condo units. Greg Waga, an architect representing Amalgamated Bank and building manager Joe LoMonaco, presented a plan to the Redevelopment Agency tonight for a total of 20 units on the top floor along with a club room with a small kitchenette, a business center/game room and a gym.

Of the 20 units, 18 would be one-bedroom units (roughly 840 gross square feet, compared to 820 in a typical Carriage City unit) and two would be two-bedroom units (one on either corner). The amenities would run along the Irving Street/train station side of the building. Much of the plumbing and electrical work that already had been done likely will be removed and replaced throughout the top floor to accommodate the new design, Waga said. The plan was arrived at after six weeks of meetings and seven layouts, he said.

Commissioner Matt Dobrowloski asked about the possibility of a long-anticipated rooftop cafe. Waga said there is the ability to install a small, serving kitchen (no cooking) for the top floor and while he anticipates possibly  doing something in the spring, it’s still uncertain. “We’ll see how this goes first,” he said, referring to the penthouse floor designs. He did say that the rooftop space has the capacity for 238 people with tables and chairs, and a standing room capacity of 530, based on the state’s International Building Codes.

The original plan for Carriage City Plaza was 222 units, with a maximum of 225 allowed under the redevelopment plan. The 20 units on the top floor would push the total to 232 units in the building, which would required an amendment to the redevelopment plan to accommodate the additional seven units.

The amendment would have to get approval from the Redevelopment Agency (December at the earliest since November’s meeting has been canceled), and then a recommendation by the Planning Board (at the earliest mid-December, if there is a meeting). The City Council then would have to introduce it before holding a public hearing at the following meeting where a vote would take place. In this scenario, the earliest approvals could be granted would be February.

About 62 units at SkyView at Carriage City Plaza sold as private condos. The remaining 160 unsold units went into foreclosure two years ago before being acquired about a year ago and are now being leased. The new ownership also owns the ground-floor retail and hotel space.