Forest City’s proposed building at 300 Massachusetts Avenue would rise to 128 feet at its tallest penthouse, eight feet taller than the penthouse on the Novartis building, a block to the south. 300 Mass. Ave. will have a variety of different heights, with including a lower 65-foot section adjacent to Random Hall, a 94-foot section for most of the width (with a 123-foot penthouse), and a 128-foot tower section. Rooftop mechanicals would be above these heights.