According to Official Guinness Records,
The largest temporary stage measures 25,549.02 m² (275,007.44 ft²) and was built by Karl’s Event Services (USA), Frieze (UK) and Production Glue (USA) at Randall’s Island in New York, New York, USA in May 2012.
For a complete list of 2012 records, please visit 2012 Guinness Records in United States.