James L. Purdy, the original owner of this farmstead, decided to build an octagonal barn after seeing one on a trip to Iowa. After returning to Gagetown, he hired the Munro Brothers, local builders who had previously built the elegant home on his country property, to recreate one for him. According to Cora's diary, construction on James' "Air Castle" began in 1923 and was completed in 1924. The barn measures 102 feet across and 70 feet high, with each wall 24 feet to the eave and 42 feet 6 inches wide. Its three-stage roof with dormers and 32 nine-light windows is unusual because most octagonal barns have a gambrel roof without roof windows. Inside are a sophisticated ventilation system, a circular hay track with a Ney Brand hay carrier, and a 29-foot-deep mow on the north and south sides. At the time, state and federal agriculture departments promoted round and octagonal barns as the barn of the future because they provided more square footage from the same amount of building material than a typical rectangular gambrel-roof barn.