Sarah Susanka has enough star power to have appeared on "The Oprah Winfrey Show." She has designed about 300 houses in the 15 years she has been practicing in Minneapolis, but her current renown speaks to the power of her ideas, not a particular building. The essence of her message: What makes us love one house over another is the quality of the space, not the quantity.

Though pursuing the "most wonderful space" rather than "the biggest space" is not the way most people approach building a house, Susanka asserts that it produces better results--a house that makes the occupant feel good. As she laid out in "The Not So Big House" (Taunton Press, $30), published in August 1998, the budget to build a big house would pay for a smaller one with spaces that could be used every day. And those spaces could be embellished with details that add character--"a beautiful stair railing, well-crafted moldings around windows and doors, and useful, finely tailored built-ins."

What does a "smaller house with a big-house budget" look and feel like? Life magazine's 1999 Dream House Project presented the opportunity to see the theory in reality, with two Minneapolis houses that Susanka's architectural firm designed and built before the 42-year-old architect resigned in June to concentrate on writing and lecturing.

Life editor Melissa Stanton directed the architects to come up with a 2,100-square-foot, four-bedroom house for a family of four--which, according to the National Association of Home Builders, is 90 square feet smaller than today's average new house. The design was to accommodate a household with small children or teenagers, and was to include a place for working at home, entertaining, an eat-in kitchen "suitable for socializing and more than one cook" and lots of closets and accessible storage space.

In short, the design was to include what home buyers everywhere want. In the end, the architects--Mulfinger, Susanka, Mahady & Partners Inc., now SALA Architects Inc.--designed two houses. The first, the Back to Basics House, came in at 1,915 square feet. A second, more elaborate Whole Nine Yards House was larger and included even more of what buyers say they want.

The conservative, traditional center-hall house so favored by Washington area home buyers is nowhere in sight in either house, even though the center hallway is still there.

The difference is that the walls that rigidly defined the spaces and their uses are gone, the stairs have been moved to one side, and half the living room (which was always too big anyway) is enclosed. What's left is a large, informal open space defined by function (dining, cooking and sitting) and by detail (differing ceiling heights, finishes, color, columns and wood flooring patterns).

The enclosed room (the "away room") is a multipurpose space that could be used as a home office, media room, guest room or adult sitting area.

The second floor has three bedrooms, two baths, laundry room and a large, 450-square-foot unfinished space over the garage.

The most pronounced exterior feature of both houses is a steeply sloping roof--the pitch is about twice as steep as most roofs in this area--that seems to envelop the house beneath it. Tucked up in its upper reaches is a small crow's-nest type of attic that was finished as a children's play space in one of the houses.

While Washington buyers would doubtless be intrigued with Life's 1999 Dream Houses, size would be a concern. The Back to Basics House has less than 2,000 square feet on the upper two floors (there's an undeveloped lower level), and that is small by Washington standards. A professional couple might find it ideal, but Life's hypothetical family of four would feel cramped.

Size notwithstanding, the details of the Basics House are winning. All the wood trim, as well as the built-in desks and the custom cabinetry in the kitchen and dining area, is clear maple. Most of the flooring on the main level is bamboo. A deep aubergine was used for the doors, windows and occasional wall accents. Window seats are tucked in here and there, and the low wall separating the entry foyer from the dining area has a large, curved cutout.

The Whole Nine Yards House has essentially the same plan, but it's 400 square feet larger, and most households of four, even those with young children, would feel comfortable here. The major difference between the two houses, however, is not size but detailing.

The Nine Yards House has unusual types of wood everywhere. The floors are red birch, sawed from 100-year-old timbers retrieved from Lake Superior. The trim around all the doors, the stair rails and the counters of the built-ins in the living room are dark walnut. Many of the cabinet doors in the main living area are faced with burled bird's-eye maple. Some of the ceilings are also red birch, and each of the three bedrooms has a cedar-paneled wall. At the base of the stairs, the red birch treads morph into maple bookshelves that in turn form the back of a built-in sofa with side tables.

Another concern for everyday living is the degree of openness in the main living area in these two houses. Because most of the first floor is visible from the entry foyer, the house would have to be cleaned up before guests arrived. And using all the spaces every day is not the same as sharing them every day. For a busy family, the communal aspect of the large open area could make controlling the inevitable clutter a daunting task.

For most home buyers, though, any shortcomings of the plan are minor when compared with the cost of these two houses. The Back to Basics House sold for $496,000, and the Whole Nine Yards House for $720,000. How is this possible?

Most of the answer is in the details. Those nooks and crannies, window seats and hideaway cabinets for TVs, unusual woods and other details--all of them add character but they also add to the cost. The craftsmanship required to build a house with this level of detail is also expensive. For example, the doors, window sashes and various trim details in the Basics House were painted by a highly compensated "Leonardo da Vinci of house painters" whose work is so flawless it appeared to have been done in a factory by a machine rather than by human hand.

The Nine Yards House was $224,000 more in sale price than the Basics House in part because it sits on a larger, more expensive lot ($150,000 as opposed to $87,000) that required trickier site work. There were also an added back porch and the crow's-nest attic that can be reached by a ship's ladder. The additional 400 square feet also added to the cost, but most of the difference was in the finish materials and the labor-intensive detailing.

The difference in the exterior treatments of the two houses also affected the cost of each. The exterior of the Basics House was utilitarian cement board, but the Nine Yards House had stucco, cedar-shingle siding and roofing, cedar siding, special wood treatment around every window and balconies with cypress decking and copper rails.

Both houses could be simplified and built for less, but even streamlined versions in the Washington area would be expensive because land prices and custom home construction prices here are high. Local home builders and architects who specialize in residential design and custom construction estimated the cost to build a modest 2,000-square-foot house could be as low as $260,000 (with very spare details and interior finishes), but $300,000 is a more realistic figure. Lots in Montgomery and Fairfax counties cost at least $200,000, bringing the total to $500,000--beyond the reach of most buyers. In Prince George's County, lots range from about $60,000 to $100,000. This would lower the total to $360,000 to $400,000, but even that is too pricey for most new-home buyers.

Those who like Susanka's approach but not the Life Dream Houses and want to hire an architect to create an entirely new design will have even higher costs. Designing a house and following it through construction, which is strongly recommended if the design is unusual and heavily detailed, would add another 7.5 percent to 15 percent, or $22,500 to $45,000, to the $300,000 construction cost for a 2,000-square-foot house.

Clearly, many who find Susanka's ideas compelling will find them possible only when they start to be embraced by production builders. Washington area production builders can deliver a finished 2,000- to 2,400-square-foot house, including the lot cost, for less than half of what a custom-built house of the same size would cost.

And if Susanka's ideas--fewer rooms, used every day, that have a higher level of detailing and finishes--become more mainstream, production builders will start incorporating them. Until then, Susanka may be right that what makes us love one house over another is the quality of the space, not the quantity. But for now, what makes us buy one house instead of another is the affordability of that space.

Architectural plans for the Life Dream Houses may be purchased through the Life Fulfillment Center; call 1-888-277-2055. One set of plans is $534, four sets $564, eight sets $609; an itemized list of materials is an additional $50.