Developer Isack Rosenberg has agreed to cut down the size of his proposed Williamsburg mixed-use development, Rose Plaza, to 776 apartments from 801, as a concession to the City Council members who will vote on his plan this month. Rosenberg’s olive branch also comes with an 8 percent uptick in the number of affordable housing units, resulting in 28 percent of the development earmarked for low-income units. But this isn’t enough to Council member Steve Levin, who wants to see 30 percent of the residential units set aside for low-income use and is demanding the inclusion of four-bedroom units, which aren’t on the docket at the moment. “The community board and the borough president specifically asked for this,” Levin said at a council land use committee meeting today. Rosenberg, who saw his Warehouse 11 evade bankruptcy last month, will likely see the committee vote before April 14.