"It's hard to pin down the cost of the seismic strengthening and restoration.
"We have always taken the view that the old girl has probably got a few surprises for us."
"But the driver for all of this is that people love the building."
Mr Bates said the trust was grateful to the former Waitakere City Council, which owned the building from 1983, for recommending the project to its successor for priority in the funding queue.
"We are hopeful of getting $5 million to $6 million from the Portage Licensing Trust, which has expressed strong support and we have a firm commitment from the ASB Trust for $750,000."
A feature of the design by Mitchell and Stout Architects is to remove old top floor additions for a rooftop terrace.
This viewing area was a popular feature when the Mediterranean-style building was a luxury hotel. It has also been a nightclub, a school for the deaf and an Education Department training centre.
The present gallery is in the old hotel dining room and cannot offer the controlled environment that major galleries expect when lending their works.