Winston-Salem Mayor Allen Joines announced Thursday that local business leader Don Flow and Charlotte-based developer Grubb Properties will redevelop the former GMAC building and an adjacent site extending to Fourth Street into a business center with retail spaces and apartments. Flow will buy the 18-story GMAC building, to which he plans to relocate all Flow Companies corporate services that are currently housed at locations throughout North Carolina and Virginia. The primary focus of the remaining floors of the building will be on attracting start-up and early-stage growth companies by offering extremely affordable space, officials said. The tower renovation would start soon after the Flow purchase closes, officials said, with occupancy beginning in late summer. In a second project, Grubb will develop a $48 million residential and retail project on the site just south of the tower, including the surface parking lot. The project will include 240 residential units and storefronts along Fourth Street. Grubb has committed to making 30 percent of the housing units affordable to working people, the city said.