The grandstand, steppings and first lift shaft are all now in place, designed by Capita Bobrowski. The structure will be complete by March 2009, in good time for next year's Derby.
11,000 spectators will fit inside the new building, with a further 4,300 on the steppings. Inside will be the 960 sq m 'Oaks Hall', available for hire.
Balconies have been designed to overlook the racecourse and offer panoramic views across London.
The Grandstand is part of a major £27.6M redevelopment, to include a new 120 bedroom hotel.