So far, workers have removed soil from the garden and a tree growing through the centre of the roof has been pruned to provide access.
Brickwork edging and other decorative elements have been removed and stored and the rest of the damaged roof dismantled.
Council infrastructure and asset manager Andy Finch said water damage to the building was not as serious as feared.
Reconstruction of the roof would take about two weeks and would include improved lining techniques to protect the interior of the building.
The brickwork edging would be reinstalled and the rooftop garden filled with soil and replanted by the end of the month.
The toilets would reopen in time for the official opening of the new Te Hononga community hub in September.