CONSTRUCTION has begun on a 50-storey commercial complex on the former site of the Lee Gardens' Hotel in Causeway Bay. Pauline Wong, director of site owner Hysan Development, said final plans for the building were now awaiting approval by government planners. She expected a final decision in about a month's time. The single-block commercial building has a plot ratio of 15 and will include retail shopping space. Hysan officials said they would also construct a walkway linking the new building to the adjacent Caroline Centre. The building, which will feature between 800,000 and 900,000 sq ft of office space, is expected to be ready for occupancy some time in 1996.