The public car park is just off the Upper Newtownards Road, one of the main routes into the city.
Thousands of wooden pallets are now piled up where previously there were parked cars.
The bonfire makers are involved in a dispute with the city council over the storing of pallets.
They say the council collected pallets from the area earlier this year, agreed to store them and return them this month but failed to do so.
Bonfire builder Macauley McKinney, 21, said: "We had an agreement with the council that they were going to store the pallets in a safe place, and now because the agreement was broken, they've let us down."
Belfast City Council is not commenting in detail on the issue, as an investigation has been called into the storing of pallets.
A spokesperson said: "It was agreed at a meeting of Belfast City Council's Strategic Policy and Resources Committee on Friday that an investigation and full review, led by the chief executive with independent input, would be carried out into the issue of collection and storage of bonfire material, and the future approach of bonfires across the city."
The committee's decision needs to be approved at a full council meeting next week.
Traditionally, bonfires are lit in many loyalist areas of Northern Ireland on the "eleventh night" - the eve of the Twelfth of July, an annual celebration to mark William of Orange's victory over King James II at the Battle of the Boyne in 1690.
A car park in east Belfast has been closed to the public by young men building bonfires.