Two designs for Wellington's movie museum and conference centre near Te Papa have been released.
One will cost $135 million - the figure the council agreed earlier this year. The other, with a more detailed exterior, comes in at $150m.
Both designs are the same on the inside.
The city's deputy mayor and Wellington mayoral candidate Justin Lester said he favoured the more expensive option and wanted other councillors to do the same.
"It's quite a spectacular design representing Te Upoko o te Ika Māui - the head of the fish of Maui.
"It's a one-of-a-kind experience and I think it needs a one-of-a-kind building, and I think that's what we're looking at."
The building would be clad in aluminium panels designed to mimic the scales of a fish.
Mr Lester said the details would be debated and decided by councillors in a public-excluded part of next week's council meeting.
He said the extra cost was still within the broad budget set this year.
"We wanted to look at options to improve the quality of the building and design.
"Because it's such a special building, quite internationally significant we thought we could possibly do better, and should probably do better.
"We're going to have people travelling from all across the world to come and see and experience the location. We tasked the architects to come up with something special and I think they've done that," Mr Lester said.
The building will 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.