The walls of the new building on top of Snowdon will be built from Welsh granite, it has been confirmed.
The new visitor centre and cafe will be built during 2007
It follows controversy over an earlier decision to use stone imported from Portugal for the roof.
The Snowdonia National Park Authority decision to use a local supplier will add £56,000 to the £8.3m costs.
Chief executive Aneurin Phillips said 60% of the contract will now come from Wales, which was "quite an achievement" because of the unique location.
A special authority meeting decided that granite from Cwt Y Bugail quarry near Blaenau Ffestiniog will be used for the walls and exterior floors of the new summit building.
Work is just beginning on site, but in July there was criticism when it was announced Portuguese stone would be imported for the roof.
Some local people who contributed to a fundraising appeal were annoyed about the foreign imports.
On Wednesday park authority members approved an officers' recommendation to spend an extra £56,000 to allow the contractor to use locally sourced material for the walls and exterior flooring.
"It has been a long, difficult and complex process," said Mr Phillips.
"Due to the restraints of European law, it has not been possible for us to insist that materials for the new building come from local sources.
"The contractor is aware of the fact that as an authority we are extremely eager to use as much local material as possible.
"Unfortunately, as a public authority we cannot insist that a contactor chooses one local supplier, or favours one more than another.
But he said he was "delighted" to announce that the Snowdonia quarry will provide most of the stone for the new summit building.
Authority members were also told about progress to the project, which must be ready by the summer of 2008 to qualify for its part-funding through the European Union's Objective One programme.
The existing building, once famously described by Prince Charles as a "slum", will be demolished during the next few weeks with as much material as possible removed from the mountain before the winter.
Prefabricating the new building will also start in a warehouse on Deeside in the next few weeks.
The saga of a new building has already run for almost five years when a feasibility study was first considered.
After a public appeal which collected almost £350,000, it was announced at the end of last year that the park had raised enough money to replace the old building.