TRY before you buy is a concept unheard of by prospective Hongkong buyers of commercial and residential property in China. But, for the first time in the territory, would-be purchasers can see exactly what they will be getting for their money. Innovative International (Hongkong) has built full-size show flats for exhibition to clients interested in buying units in Innotec Tower, its HK$250 million commercial and residential twin-tower development in Tianjin. The development is due for completion in 1995. The three-day exhibition will be held in Forum IV of the Lee Gardens Hotel in Causeway Bay from Friday to Sunday between 9 am and 7 pm each day. Show flats have been built at Innovative's Hunghom headquarters and guests will be taken back and forth by a special fleet of buses. The chairman of Innovative, Mr Chang Lien-hing, said: ''Our exhibition will be the first time that people interested in a property in China will be able to actually see a full-scale show flat located right here in Hongkong. ''Tianjin is China's third biggest city, and the number of foreign-invested enterprises establishing presences there is growing quickly and creating a high demand for quality offices and luxury accommodation. ''Most of that demand is from expatriates from Hongkong, Taiwan, South Korea, Japan, and the US who are looking for the convenience of living adjacent to their place of business,'' he said. Designed by Hongkong-based firm John Lei Architects, Innotec Tower will be a self-contained development comprising a three-storey retail podium with shopping and dining facilities, topped by a 23-storey commercial block and a 26-storey residential block. The development is the only Grade A commercial and residential complex in Tianjin and will be located in one of the city's prime districts, only eight miles from Tianjin International Airport and less than a 60-minute drive from the city's new port and container terminal. Innotec Tower is to feature a glass-topped atrium in the lobby, club house and health facilities, STAR TV, IDD phone lines, and underground parking. In the office tower, each 220-square-metre unit will come with fittings, including individually controlled central air-conditioning and heating. Residential units range in size from 100 to 191 sq m. Tianjin is a major transport hub for northern China, with extensive rail, air, road and shipping facilities.