As designer of Poplar Forest, one of the first octagonal houses in America, Thomas Jefferson probably would have liked Susan Cooper’s house in McLean.

Seen from the roadway, Cooper’s eight-sided house looks farm-friendly, or maybe nautical, like the lighthouse in St. Michaels, Md. — crisp white brick against the surrounding lawn, with a red standing-seam metal roof and a porch that encircles the house at ground level. A second octagonal level sits atop the first, set a few feet back from the edge of the roof below. Popping up in the middle of this confection is a windowed belvedere topped by a cupola, again echoing the eight-sided shape. An oversize glass-topped breezeway attaches the left side of the house to a two-car garage.

But it’s when you walk into the house that you feel the joy of the design and understand why Jefferson thought it a sublime arrangement for living. Stand just inside the entrance, and in front of you is a center atrium drenched in light from the windows of the belvedere two stories above. Look straight ahead, past the atrium, and you see through to the dining room and then through the French doors to the porch and garden beyond.

Still standing just inside the front door, a glance to the right reveals part of the living room; look to the left, and there’s the kitchen counter in the middle distance. None of the rooms is wholly revealed even as you enter them, letting each one borrow square footage from your imagination.

More important, though, and what so captivated our third president, is the light that floods each room from the ample windows and French doors that march around the perimeter. Walls and ceilings on the ground floor are all white. They gleam and reflect natural light because there’s a slight gloss to the painted finish.

Susan Cooper, 69, of McLean owns this 6,400-square-foot octagon-shaped house in McLean. She conceived the idea for the house about 30 years ago.

In designing Poplar Forest, Jefferson was inspired by Andrea Palladio’s 16th-century reinterpretations of Roman villas. He thought the long, windowed pavilions of the French were brilliant in the way they provided light. He absorbed these ideas and developed his octagonal plan based on Palladio’s round Temple of Vesta.

Cooper’s inspiration was also historical, but more recent and more personal. Thirty years ago, she fell in love with a round house in Marshall, Va. It belonged to her then-boyfriend. “It was really 13-sided, but it read like it was round,” she says. “I was fascinated by it.”

A few years later, Cooper asked Vienna architect Joseph Burton to design an octagon house for her. She even had a model made. Years passed, and Cooper, who helped manage her family’s commercial real estate portfolio, put the plans out for bid but couldn’t make the numbers work. When Cooper and her second husband, Carleton Cooper, wed in 1992, he wanted to keep his Arlington County house, so the octagon house plans stayed on the shelf. When Carl died several years ago, Cooper decided she needed a project.

Cooper — granddaughter of developer Ashton Jones, for whom the Ashton Heights section of Arlington is named, and daughter of Ashton Jones Jr., who developed Arlington’s upscale Country Club Hills — is now 69. She has two children from an early first marriage, three stepchildren from her second and seven grandchildren. And, since 2008, she also has had an octagon house, made to her old plan by a custom home builder, with help from Burton. (“Marty Dunn is the best contractor I’ve ever worked with.”)

The flow of the house is one reason she loves her home. As you walk into the living room, you see part of the dining room ahead and to the left; a pair of knee walls with columns separate the two spaces. From the dining room, you see a glimpse of kitchen. From the kitchen, you see back to the entryway. Furniture doesn’t hug the inner walls; it floats in each space.

All that space is possible, Burton explains, because of all-steel construction. Steel columns mark the eight spokes of the house, hidden inside the walls of the atrium, and attach to steel beams that let the ceiling soar. The second-level walkway is cantilevered. With steel construction, Burton says, “You’re free to create more open spaces.” The three levels of the house add up to 6,400 square feet.

These techniques came easily to Burton, who has worked with Cooper’s real estate business and designed such projects as the Preston King post office in the Westover section of Arlington and the Mercedes-Benz dealership in Tysons Corner.

All this industrial-strength building was supposed to have been paid for by the sale of Cooper’s previous house, in Arlington. “With the downturn in the economy,” she says, laconically, “it didn’t quite turn out that way.” The Arlington house sold in 2010 for $1.125 million. Gulp.

The outer wall of each of the eight sides of the new house is 22 feet long. Cooper’s first floor divides into four main spaces, just as Jefferson’s did (but Cooper did not install alcove beds around the first floor the way Jefferson did). A small office, a pantry and a powder room are tucked away along the perimeter so as not to interrupt the flow.

The second floor has the same arrangement of four spaces, for three guest rooms and a master bedroom, with bathrooms worked into each bedroom’s space. “People told me an octagon shape would make furniture layout difficult, but it didn’t really,” says Cooper, showing one of the guest rooms. Two are big enough for queen-size beds and nightstands, a chest and an easy chair; one is kitted out with twin beds and chest.

All the spaces are not equal, however: The master bedroom suite, with its large, en suite bathroom, wraps around more than a quarter of the upstairs.

Upstairs and down, the rooms seem to have as much furniture as necessary and no more. A long L of a sofa and a couple of side chairs are enough for the living room, which is oriented toward a fireplace on the outer wall. There are built-in display shelves on either side. The dining room holds a 52-inch round table, but the space can accommodate two more tables for entertaining. Closets that disappear into one wall of the dining room hold a splash of colorful glassware and dishes. In the adjacent living room, a closet holds the sound system and extra bridge chairs.

If these rooms were obviously made for entertaining, Cooper is happy to oblige, with “one or two couples over for dinner just about every week,” she says. There’s a lot of family entertaining, and Cooper has opened the house to the McLean Woman’s Club. Then there’s her annual “hen party,” when female friends from years past come together: 19 for dinner one night, 35 for dinner the next day.

“I don’t do anything formal,” Cooper says. “I just want to give people a good time.” Meals, she says, are always buffets, laid out on the kitchen peninsula.

The ground floor is covered in whitewashed Saltillo tile, a Mexican terra cotta tile that Cooper loved in her previous house. Eight strips of tile in a contrasting color radiate from the center of the atrium like spokes on a wheel.

The atrium is interrupted by something Jefferson didn’t have: an elevator, housed in what looks like a structure made of stacked French doors. (Jefferson, that inveterate tinkerer, would no doubt have been suitably impressed. His home at Monticello is famous for the dumbwaiter he fashioned to bring up wine from his cellar.) Curling around the opposite wall of the atrium is a staircase that leads to the bedroom level.

But the elevator also goes down to a walk-out basement that’s every bit as bright as the main level (it gets a little halogen help). The ceiling is nine feet tall. The idea, Cooper says, was for the space, a family room, to have “as nice a quality down here as it does upstairs.”

Which leads you to Cooper’s weakness for murals. Painted on the wall behind the family room sofa is essentially the same garden view you will get from this spot upstairs. On another wall is yet another garden view.

The conceit is not a shock, though, because in the living room, you will have already seen Renoir’s “Luncheon of the Boating Party” splashed on the wall behind the sofa. Renoir’s models in the lively dining scene have been replaced with the faces of Cooper’s children and their spouses. In the atrium, guests stepping out of the elevator are greeted by another Renoir: the instantly recognizable dancing couple in “Dancing at Bougival.” Both were painted by muralist Thomas Mullany of Washington, Va.

More-conventional works hang on the walls upstairs in a kind of gallery created by the mezzanine that winds around the atrium. These were done by watercolorist Linda Griffin, a Washington area native living in North Carolina.

It was while walking around the gallery the day she moved in, after 30 years of waiting and 11 / 2 years of construction, that Cooper had a sense of belonging wash over her. “I’m home,” she thought.

But that’s not the end of the story. After June visits from various children and her hen party, July will bring a new beginning to the McLean octagon house. In the terraced rear garden, Cooper will marry Tony Jordano, 75, an engineer formerly at IBM and still engaged in systems engineering for government contractors. The octagon house has already embraced Jordano, his four children and seven grandchildren.

Cooper and Jordano met online. No doubt the ever-inventive Jefferson would have approved of that, too.