Building institutions

"David Rockefeller, who died last March, was one of those rare multifaceted individuals who excelled at almost everything he did. He was a renowned banker, entrepreneur, civic leader, philanthropist, preservationist and developer, among many other things. He loved building institutions as much as he loved foreign policy and economics, but above all he loved to collect." (CNN.)

Is "building" a noun or a verb in the passage above?