Suspended on a platform the 20-year-old trainee civil engineer used a spanner to twist tight the last roof bolt at The Hydro Arena on the banks of the Clyde.
It was billed as a traditional topping out ceremony only it took place 27 meters up in the air on a concrete platform.
John, from Knightswood, was joined by Gordon Matheson, leader of Glasgow City Council, Sir Ian Grant, chairman of the SECC and its chief executive John Sharkey. Also there was Gordon Anderson executive general manager of Lend Lease which is building the new £116 million arena.
Putting the roof on the new arena has been a major engineering feat; at its highest point is twice as tall as Glasgow's Queen Street Railway Station.
John has worked on the project since it work began in April last year.
He said: "Working at The Hydro has been a fantastic opportunity for me and has given me a foot in the door in the industry, one for which I am very grateful."
He's loved every minute of it and added: "My long-term plan is to study for a degree in civil engineering at Glasgow Caledonian University."
The Hydro will be the biggest venue of its type in Scotland when it opens in September and has the potential to generate around £131m every year in extra income for Glasgow.
It will provide an ideal stage for some of the world's top music and entertainment acts.
Already Lend Lease chiefs are predicting it will be among the five busiest venues globally and will be on par with London's 02 and New York's famous Madison Square Garden.
Gordon Anderson, of Lend Lease, said: "The completion of The Hydro's roof structure is the most complex feat of engineering in Scotland this year and today's topping out is major step forward in The Hydro's construction process."
SECC chairman Sir Ian Grant said: "The topping out ceremony today signifies just how close we are to the completion of a world class entertainment arena for Scotland."
Council leader Gordon Matheson recognises the importance the arena will have in enhancing Glasgow's reputation as a venue for world-class entertainment.
He said: "The Hydro takes Glasgow's global offer for entertainments and events to an even higher level.
"It's going to be as iconic as its neighbour, the Armadillo, and it will play a key role in Glasgow's Commonwealth Games in 2014.
"I want to congratulate Lend Lease on a superb engineering achievement.
"I can't wait to see this amazing building lit up at night as it hosts many thousands of people.