The museum village is home to a unique collection of NZ Historic Places Trust listed buildings and historic horse-drawn vehicles, machinery and artefacts.
Some of the collection was found to be at risk because of storage conditions so almost three years ago the trust began planning a better space to house the collection and make it more accessible to the public.
Mr Gilberthorpe said some items had been stored in sheds, where they were susceptible to the elements and insects, especially if made of wood or metal.
"We are never going to be the same as the big museums where they have air temperature control ... we were just trying to create a building that has reasonably stable, clean dry conditions."
An important room in the new building was the collection storage room where they could catalogue and restore items in a stable environment, he said.
Craig Turvey of Masterton's 3D Creative designed the exhibition with research by Ian Wards, an expert in museum development.
Mr Gilberthorpe said not every part of the collection will be on display but the exhibits can evolve and change over time.
He said what had been achieved for the village over the last 45 years was amazing and the trust was building on that.
Construction started last November and the trust fund-raised close to $1 million.
Museum trustee Leigh Hay said the Friends of Cobblestones volunteer group had done a lot of work and the grounds were looking beautiful for the opening.
Mr Gilberthorpe said there were between 3000-4000 visitors a year and he would like to see that figure at least doubled.
The opening begins at 10am with pony rides, vintage cars, spinners and weavers, blade shearing, Father Christmas, printworks, vintage engines, a sausage sizzle, and more.