Hastings Mayor Sandra Hazlehurst said the steel trusses, which were built by a local engineer, were an outstanding engineering structure.
"This is a wonderful opportunity to reuse the innovative structures for other purposes in the future."
The work on the Plaza would be done in conjunction with the earthquake-strengthening of the neighbouring Hawke's Bay Opera House. The two projects would be carefully choreographed to limit impacts on the road-using public and to get best value for money, Mrs Banks said.
Once the floor was levelled, a crane would be sited inside the Plaza to help strengthen the roof.
The strengthening and refitting of a new roof would start on March 12 and would take about three months to complete.
"There will be a slight change in the profile of the Opera House roof towards the rear of the building but apart from that there will be no noticeable change.
"All work being carried out on the Opera House is being closely monitored and approved by Heritage New Zealand who have a representative on the project team."
By April the detailed design of the new Plaza roof will be finished and then constructed on site, with the Plaza expected to re-open in December 2018.
The Opera House was expected to reopen towards the end of 2019.