A WA Labor election commitment to provide $10 million for a major rooftop development at the Art Gallery of Western Australia (AGWA) is being regarded as a done deal, with plans unveiled for the makeover.

The proposed public and private partnership is set to turn the AGWA's unused rooftop into an outdoor cinema, performance and events space and restaurant at a cost of $25 million.

Amid falling visitor numbers at the gallery, the aim is for the development to be completed in time for the institution's 125th anniversary in 2020.

The new rooftop will be accessible after hours by an external lift and will have a newly commissioned work by a major artist, an outdoor art display and a community gathering space.

AGWA director Stefano Carboni said he presented the plans to ousted Premier Colin Barnett seven years ago and more recently to outgoing Arts Minister John Day, but they did not progress.

Mr Carboni said he briefed members of Labor's shadow cabinet about the proposal in December last year, and it soon became the top listed election commitment under the party's 'Supporting the arts and creative industries' platform.

The $25 million redevelopment will include an open air cinema and event spaces. ( Supplied: AGWA )

He said while he was yet to speak to the incoming McGowan government, he expected the new arts minister to honour the commitment.

"We felt it was appropriate to go public with the idea now that the election has taken place. So certainly we will be in the new minister's office very shortly to talk about it," Mr Carboni said.

"We can start implementing a few things now."

The Labor government's cabinet is yet to be confirmed, although the shadow arts spokeswoman had been Michelle Roberts.

Rooftop to provide much needed income

Mr Carboni said the development would provide an opportunity to provide new sources of income for the gallery, which has struggled with funding cuts in recent years

"[It will] make it more of a destination that is open for business from 10:00 in the morning to after hours and evening events," he said.

The project is modular and is planned to be implemented without any significant gallery closure.

Gallery chiefs say the development will offer a great city view and improve accessibility. ( 720 ABC Perth: Emma Wynne )

AGWA board chairman Sam Walsh acknowledged the gallery was facing financial difficulties.

"In challenging financial times the rooftop development and the other significant enhancements are an exciting and achievable goal for the gallery," he said.

"The vision for the rooftop was left incomplete when the gallery opened its new building in 1979. It's great, 40 years later, to be able to plan completing the job in such style.

"It will be one of the best city views in Australia and a go-to place for something extraordinary in the WA arts scene."

Both new spaces will welcome potential PIAF and Fringe World events and the current staff car park on Beaufort Street will be changed into a garden space also dedicated arts displays.

The WA Chamber of Arts and Culture chairwoman Helen Cook welcomed the plans and said it would help to increase the vitality of artistic life in WA.