The school had recent experience of using prefabricated buildings in 2012-2013, but Mr Brown said it could have cost about $500,000 for temporary accommodation during the new project.
"That's dead money," he said.
Mr Brown said the "big challenge" was to provide classrooms - otherwise known as MLEs (Modern Learning Environments) - suitable to the changes of the next 50 years.
Among the reasons for the replacement of Armour Block, built in the 1960s, was its unsuitable for Wi-Fi. It has also been leaking, as Minister of Education Hekia Parata discovered when she caught a few drips from the ceiling as she entered the building during a visit last week.
A school group will visit other recently-built schools in Bay of Plenty and Auckland to develop ideas and advice on ensuring the capabilities of the new buildings well into the 21st century.
The school currently has 55 classrooms and and a roll of about 1220, but the roll is not forecast to increase in the foreseeable future. The size of the project mirrors the rebuilding of much of Karamu High School, where 22 classrooms have been replaced and other facilities upgraded in a project costing about $7.6 million.