Ridley, a former Atkins director and chairman of QS Faithful & Gould, said he intended to grow the company organically and through acquisitions.
He said: "I am thinking in terms of quantity surveying, building surveying and planning and scheduling.
"Basically, we want to offer commercial support services in the construction industry.
On the subject of acquisitions, he said his model was Faithful & Gould's purchase of fellow QS Silk & Frazier in 1998.
"It was an excellent buy; it was in a different sector and region and the partners fitted into the culture. It was a smaller Faithful & Gould.
"We are looking for smaller and medium-sized businesses that want to expand a bit, to get involved in a bigger pot. They will not necessarily be quantity surveyors."
However, Ridley added that he was also hoping to promote organic growth at the £2.7m-turnover firm, which operates in the UK, Asia and North America.
He said: "I have got one new client in and have four or five other good leads. You have got to have organic growth – it is the most important part of any expansion."
Ridley said that he was also looking to bring in new people. "The most important leg to the growth is people. As far as growth goes I have seen it all before – I have seen what works and what doesn't."
Ridley, 60, said he planned to stay at the business for five years. He said: "We will look at what we have achieved in five years."
NBA managing director Peter Elliott-Hughes said the firm would now be more aggressive in approaching possible acquisitions.
He said: "Up until now we have been naturally cautious about acquisitions.
"We want to be more aggressive – the type of business we are looking at has to perform."
Elliott-Hughes said Ridley had brought a formidable contacts book with him. He said: "I've never known someone as well connected as David."