THE APARTMENT: Estate condition. Original classic six home, now five rooms, includes living room with wood-burning fireplace, formal dining room, two bedrooms each with en suite bath, eat-in-kitchen, powder room. Beautiful north and south light. Overlooks a fully planted garden. Offering includes two double staff rooms, each with bath, on the lobby level. (For each double staff room, there are 54 shares and additional maintenance of $984.) THE BUILDING: Steps off Park Avenue, Millan House was built by John D. Rockefeller Jr. in 1931. A co-operative since 1947, Millan House consists of two separate buildings connected by an extraordinary two-level Italianate interior garden courtyard, with a wonderful fountain and seating areas. Designed by architect Andrew J. Thomas with 57 apartments, the buildings are of general Romanesque character and covered with unique carved animal ornamentation. Pied-a-terre purchasers and pets are welcome. Co-Exclusive with Corcoran