Donnell, who had studied architecture at Harvard, planned to gut the building and construct a new, modern office complex inside the historic shell. Failing to obtain financing for the remodeling, he embarked instead on an incremental, "pay as you go" project to restore the Monadnock to its original condition in painstaking detail. The project was, according to historian Donald Miller, the most comprehensive skyscraper restoration ever attempted at the time; it took thirteen years to complete. Working from original drawings discovered at the Art Institute of Chicago, and two old photographs, Donnell and John Vinci, one of the nation's leading preservation architects, restored the building to its condition when first constructed, before any modernizations, working piecemeal as offices became vacant.