The Wellington City Council has chosen a $150 million sculptural design for the city's movie museum and convention centre.
Councillors unanimously agreed to go with the more expensive design, in a debate which excluded the public.
Earlier this year, it provisionally approved $135m for the project.
Deputy mayor Justin Lester said the increased cost could be absorbed into the annual plan.
The building would be clad in aluminium panels designed to mimic the scales of a fish.
Mr Lester said negotiations with Peter Jackson's movie museum company had a November deadline, at which point an edited version of the business case for the project would be released.
He said work on the building should start early next year.
The building would be owned by the council, and the movie museum would be a tenant on the first two floors, with the 1000-plus-seat convention centre on the top floor.