The building will house Fletcher Reinforcing, Easysteel, and Dimond Roofing. Moving there will cost Fletcher Steel $2.5million.
Fletcher Steel head of marketing Neil Watson said it would be the company's most modern building in New Zealand.
This was the first time three Fletcher Steel businesses had operated out of one building, and such an operation would not be possible in Auckland or Wellington.
"It makes perfect sense, depending on the size of the town," Mr Watson said.
The first business moving in was Dimond Roofing, which would be open from April 10, followed by Easysteel on April 17 and Fletcher Reinforcing in mid-May.
It would be good for the city, not just for Fletcher Steel, especially with the amount of construction work coming up in Dunedin, Mr Watson said.
Dimond Roofing area sales manager Chris Silcock said construction began last October.
The Carisbrook turnstiles were being kept, and a mural would be painted on the outside wall.
Thirty people would work in the building, but staff numbers could swell once it opened, Mr Watson said.
The building was being constructed by Calder Stewart.
Once everything was moved in, the building would inevitably become noisier and busier, but Fletcher Steel had taken into account the fact they were operating close to people's houses, Mr Watson said.
"We certainly considered the residential area we are in."
He said the new building would be "a million times better" than Fletcher Steel's premises Fletcher Reinforcing, in Green Island, and the city's Dimond Steel and Easysteel.
