But the New Zealand building industry is characterised by booms and busts, he says, making it important to diversify the design practice and grow its income from Australia.
Managing director Peter Marshall says the firm is building on lessons learned from opening new offices in New Zealand.
The economic cycles of each city are slightly out of sync with each other, he says.
When building activity was quiet in Wellington it was often rocketing along in Auckland.
"It was just a way for us to try to mitigate some of the peaks and troughs that are inherent in our industry," Marshall says.
While Warren and Mahoney's New Zealand portfolio brims with high-profile public projects - the Supreme Court building and Westpac Trust Stadium in Wellington; Christchurch's Town Hall; and the Maidment Theatre, Telecom Place and Waitakere Trusts Stadium in Auckland - the focus for Australia will initially be on several niche areas.
The firm has built a strong reputation for "customer experience" design, a growing trend for institutions to rethink the way in which they deal with customers.
"People come into a [bank] branch not because they want to transact, because they do that at home online, they come in because they want information, they want advice, they want to validate something or they want to prepare to make a transaction," says Coop. In practice this means that eyeballing a row of tellers is out, replaced with a chat around a laptop on a cosy couch.
The BNZ is typical of Warren and Mahoney's growing portfolio of Australian clients, where work here has impressed its Australian parent, the National Australia Bank, and led to further projects across the Tasman.
Coop says the firm has secured three significant partnership commissions with a lifespan of up to five years, all thanks to its growing reputation in customer experience design, giving it the confidence it can succeed over a longer period in Australia.
Warren and Mahoney has also built up a portfolio of work from its involvement in bridge design and other elements on significant infrastructure projects, including Auckland's Victoria Park tunnel and Waterview project and the MacKays to Peka Peka road north of Wellington.
Coop says community expectations and the Resource Management Act are driving the introduction of architecture into infrastructure schemes, and similar opportunities exist in Australia.
He says it's not a "boots and all in the trenches play" but rather a careful move, made without compromising stability in New Zealand.
"So we're not yet imagining designing art galleries or museums in Australia," says Coop. "We're actually specifically targeting niche areas where we can compete at a level of regional excellence and secure work on merit in Australia."
It's a two-way street though.
While new Sydney-based recruits Chris Adams and Bianca Pohio, the Kiwis behind award winning Pohio Adams Architects, provide the local market knowledge, networks and nous, it is expected transtasman collaboration will bring new design ideas and talent back to New Zealand.
"In the next five years in New Zealand there is going to be growth," says Coop. "There's going to be the task of rebuilding our second major city. We are interested in ensuring we have the right resources ... to deliver."
Marshall says some people have questioned the move to Australia given the work linked with rebuilding Christchurch - Warren and Mahoney were key players in a team creating a blueprint for the city's renewal - and growth in Auckland.
"To us it's not one or the other. To us there's all the logic and reason that we've talked about, why we want to do all these things and it strengthens the practice and our offering by doing all of these aspects."
Coop says there has also been a strong tradition of creative companies succeeding overseas, something that hasn't happened with architecture.
"We just feel it's the right time for Warren and Mahoney to be taking that lead in terms of the architectural profession in New Zealand," says Coop.
"It's an intentional move and we're pretty pleased with the progress thus far but we also have our eyes open to the challenges ahead."
