and who constructed the structure?
William Henry Barlow
St Pancras railway station
 The station was designed by William Henry Barlow and constructed with a single-span iron roof. 
is london st pancras international the same as kings cross No, they both are different stations. where is the main station located? It is a central London railway terminus on Euston Road in the London Borough of Camden. when was it constructed? 1 October 1868 has there been any mention about it's designing specialty? Yes, it was constructed with a single-span iron roof.
wiki:12131738
St Pancras railway station [SEP] Introduction
The station was constructed by the Midland Railway (MR), which had an extensive network across the Midlands and the North of England, but no dedicated line into London. After rail traffic problems following the 1862 International Exhibition, the MR decided to build a connection from Bedford to London with their own terminus. The station was designed by William Henry Barlow and constructed with a single-span iron roof. Following the station's opening on 1 October 1868, the MR constructed the Midland Grand Hotel on the station's façade, which has been widely praised for its architecture and is now a Grade I listed building along with the rest of the station.