According to Official Guinness Records,
The largest Meccano structure is 28.76 m x 1.87 m x 6.22 m (94 ft 4.28 in x 6 ft 1.62 in x 20 ft 4.88 in) and was created by the School of Planning, Architecture & Civil Engineering, Queen's University Belfast (UK) in Belfast, UK, on 1 July 2015. The structure depicted a bridge and was built using 10,000 Meccano pieces.
For a complete list of 2015 records, please visit 2015 Guinness Records in United Kingdom.