Call it a mansion, or call it an estate, with more than 10,000 square feet of living space, the Fairbanks is clearly a high-class home. The combination of colonnaded entrance and rough-hewn stone exterior puts one in mind of the unpretentious solidity of a Roosevelt-era hunting lodge.

The breathtaking 20-foot-wide circular foyer, vaulted to the second floor, serves as a hub, offering five choices of direction, and it could take hours to explore all of them. Nothing is little here. Even the hallways are five feet wide.One of the most unusual features is a 27-foot-by-44-foot recreation room, larger than some homes. It includes a row of skylights and a wet bar at the far end, and a recessed fireplace that punches out one side. Fill it with bright lights and twirling dancers and you've got a ballroom. A huge sky-lit spa, with convenient bathroom, and a half-oval-shapedstudy complete this wing.

Each of the family living areas gathered together at the opposite end of the Fairbanks has its own unique features. The oddly shaped living room has a fireplace and a bay window, and the formal dining room is a perfect oval. The free-form kitchen has both a cooking island and an eating bar with a vegetable sink.

Light from another row of skylights makes the nook an ever-cheery space, and a fireplace provides additional warmth in winter. The utility room includes a pull-down ironing board.

Each of the three bedrooms downstairs has its own private bathroom, and two have walk-in closets. These rooms could easily be used as guest or servants' quarters. Three equally lavishly outfitted bedrooms are upstairs (one with a fireplace), along with a small den and an enormous master suite - a home in itself.

In addition to a sleeping space, the suite includes a sitting room, with adjacent small kitchen, his and her bathrooms (each with a bidet), and his and her closets. A novel vanity island has a double-sided mirror with basins beneath each side. Twelve-foot-wide sliding glass doors open into an elevated spa, and a small sauna adds the final luxurious touch.

For a study plan of the Fairbanks (209-13), send $7.50 to Landmark Designs, P.O. Box 2307, Eugene, OR 97402. (Be sure to specify plan name and number when ordering.) Designers, architects and readers with plans they would like to see featured also are invited to contact Landmark.