Miller told Newshub, if EQC footed the bill and accepted liability it could cost hundreds of millions, or up to a billion for the taxpayer to put it right.
"Is it $100m? $200m? $300m? I don't know."
Miller had made a public apology and Minister responsible for the EQC, Megan Woods, said she was pleased EQC had shown remorse to those affected.
Wood was aware a big bill would be coming, should the Government accept responsibility.
The cost of the problem could be at the billion-dollar margin, she said.
Woods had ordered the Treasury to forecast exactly how much the bill could be, she told Newstalk ZB
"I have asked Treasury to do some modelling around the potential liability, the broader category of repairs for the Crown.
"We know to date we have spent $270 million on fixing repairs that were not done properly in the first place."
There were 654 cases of houses that had been purchased and repairs made were faulty, or damage was not mentioned in a scoped visit to survey the house.
Wood and Minister of Justice Andrew Little would be looking into test cases to understand where the liability lied with EQC, the private insurers, contractors or the project management office.
A court would decide if the EQC had liability which could take between 12 to 18 months, Woods said.
She said it was a mess left by the last Government.
"I don't want to wake up one morning and find a billion-dollar bill on my desk that I have to go and tell the Minister of Finance about.
"I want to know what is coming and for us to have a plan in place to deal with it."
