Four-year-old Harry Finch was born with spastic diplegia cerebral palsy in his leg muscles and has recently undergone surgery in the United States.
The operation completed at St Louis Children's Hospital, Missouri, was to release the muscle tension in his legs.
Last year, Cromwell's Derek Craig discovered the challenges Harry's parents, Bex and Hayden Finch, were facing and got in touch.
The builder has built two container homes which he has on-sold, providing the total $100,000 from the sale to the family for surgery and travel costs.
Harry's father said the support had been a massive weight off the mind.
"It's amazing. It's pretty overwhelming to realise how much people had given their time and materials and donations just for a wee man in Dunedin - our son."
The project was aided by a $25,000 working bee grant from the Placemakers Foundation.
The container builds were on display for Cromwell residents over the weekend as builders on the project added finishing touches.
One 40-foot container house features a kitchen, bedroom and bathroom while the other 20-foot container can be used as a wing, with two bedrooms.
Mr Craig confirmed both container homes had been pre-sold.
"You can either choose to help or choose not to help," he said.
"I enjoy this type of thing. It's a good place to work because no-one is in it for themselves."
A "determined" Harry continued to have hour-long physio sessions four times a week to help strengthen up his muscles, Mr Finch said.
"He takes it in his stride. He's not scared of going to hospital.
"The more we work hard, the more likely he will catch up with his [twin] brother."
Placemakers' chief executive Bruce McEwen said the gesture was "pretty inspirational".
"He's taken his idea and vision and he's put a whole lot of hard work and dedication to provide this amazing outcome."
