"It's the building's fault - all the doors up there are open to the public," said the man, who spoke on condition of anonymity.
"Nothing is locked, so they need to sort their stuff out."
A Wellington-based representative of West Plaza's overseas owners, Frank Delli Cicchi, indicated surprise that the plant room was unlocked during Monday's escapade and yesterday morning, when a reporter was able to reopen its door.
He said he had since been assured by site managers the building was secure, and that contractors would be reminded to lock roof access doors behind them.
But the young man said he knew of several people who had been on the building's "observation deck", although none as foolhardy as those photographed on Monday by an office worker from a nearby skyscraper.
He had contacted the trio - who he understood to be aged 15 or 16 and from Waiheke Island - through a friend yesterday to urge them against such behaviour and had taken steps to restrict access to his Instagram photos and delete any that could be taken as encouragement to others to follow their example.
Although he had twice hung off high-rise balconies to take photographs, he had done so with the permission of tenants and with others holding on to him.
A worker in another high-rise building said the incident was not isolated and he saw a man and woman taking selfies while dangling off the top of the 14-storey President Hotel in Victoria St last week.