Museum commercial director Murray Bayly said the forest remained a "massive" success but a new roof was needed within a few years to avoid the plastic materials becoming more brittle and deteriorating.
James Crawford, of Logic Group, was undertaking project management and many alternatives had been considered, including the roof materials used at Forsyth Barr Stadium.
An option based on the current forest roof materials could also be considered.
"He has searched throughout the world for solutions," Mr Bayly said.
The new roof had to be well insulated to keep out the Dunedin cold, rain and snow, and to retain warmth and humidity.
"If we don't do that, it will cost us a lot of money."
UV light also had to be let in to enable the forest to grow.
Overseas butterfly houses and forest facilities were often in tropical countries, including the butterfly house at Singapore Airport, and did not face the technical challenges of operating in a colder climate.
It was hoped the new roof would have better insulation and improved health and safety features, including railings to protect staff who were on the roof. The aim was to provide better access so that staff could reach safely across the roof to undertake cleaning.
Otago Museum Trust Board reports have cited a range of possible prices for a replacement roof, ranging from $400,000 to $738,000 or more, and fundraising will be required.
Mr Bayly said if the money was available, a start could be made within six months and it would be good to replace the roof within about two years.
"We are looking at whole-life costs of the roofing products and improving the energy efficiency of the temperature and humidity control systems."
The museum was considering many options and did not simply want a "quick fix" that would not be sustainable in the longer term, he said.
