When Jon Gentry and Lydia Ramsey began thinking about building a house, they didn’t need to search far for a lot. Ms. Ramsey already had a place in mind: her grandparents’ forested property in Indianola, Wash., near Puget Sound, where she once played Wiffle ball and soccer, and which her parents had inherited.

“My parents live just down the street, so I spent a lot of my childhood here,” said Ms. Ramsey, 38, a folk singer-songwriter, fondly recalling how a Ping-Pong table had served as both a playing surface and dining table in her grandparents’ manufactured home.

“Grandpa always had a slamming forehand, and Grandma had this little chop backhand,” she said. “There was a lot of family love and memories already built on this land.”

She and Mr. Gentry, 43, a founding partner of the architecture firm GO’C, had spent years moving around Seattle, but were ready to put down roots and start a family. They initially thought of the half-acre lot in Indianola as a place for a weekend house. But in 2018, a new ferry started making the trip from nearby Kingston to downtown Seattle in 39 minutes. Suddenly, the idea of living there full-time seemed feasible.

From Indianola, it was a 15-minute bus ride to Kingston, which meant that Mr. Gentry could commute to his Seattle studio in about an hour. That seemed doable, even before he began working from home more often during the pandemic. After Ms. Ramsey’s parents gave them the lot in 2019, the couple spent a year drawing plans and lining up construction financing.

Faced with the opportunity to design almost anything, Mr. Gentry felt daunted. “I said to Lydia, ‘OK, you’re in client role and I’m going to do what I do as an architect and present options for you to consider,’” he said. “That took some of the weight off me.”

Those options included a wide range of building types, from a house with a conventional gable roof to one inspired by sheds. They ultimately settled on a modernist home with a flat roof. “We kept coming back to this flat roof that would give us a bonus exterior level on top: an elevated roof garden where we could hang out,” Mr. Gentry said.

The structure below the roof is a single-story, 1,700-square-foot box with floor-to-ceiling glass doors and windows that open the structure to light and air. One side of the house has a large living space that includes the kitchen, dining area and a living room with a cast-concrete fireplace and a built-in daybed in a niche with a skylight. The couple considered building a music room for Ms. Ramsey, but decided to invite her songs into the heart of the home by keeping her piano and guitars in the living room.

The other side of the house contains the primary suite, an additional bedroom and a home office for Mr. Gentry. He also added structural elements capable of supporting a second floor above the bedrooms, in case they ever want to expand.

The glass doors can open much of the house to the forest. The rest of the structure is clad in charcoal-colored brick that extends out beyond the home at either end to create two outdoor spaces: an open-air shower by the primary suite and a wood-storage area that doubles as a whiskey snug near the living room.

To keep costs down to about $600,000, most of which came from a construction loan, Mr. Gentry and Ms. Ramsey did much of the work themselves. When their builder, Sparrow Woodworks, began construction in April 2020, the couple were right there alongside the contractors, doing much of the heavy lifting.

Mr. Gentry and Ms. Ramsey built the concrete formwork themselves, from the footings to the chimney; they cut down a few of the surrounding Douglas fir trees, then milled and finished them on site to clad interior ceilings and make kitchen shelves; and Ms. Ramsey lugged bricks while serving as the mason’s assistant.

Did they ever have second thoughts about their extreme D.I.Y. project? “There were some times when it was raining and muddy, and we were setting form panels, and I was trying to get a plumb level to hit a spot where a grid line was supposed to be,” Mr. Gentry conceded.

But they were determined to see it through. “Because we went into this project with the mentality that we wanted to do something extraordinary that would be part of our story, we were really all in,” Ms. Ramsey said.

Mr. Gentry added: “We were going to honor the land and your grandparents.”

They moved into the house in October 2021. In December 2022, Ms. Ramsey delivered their son, Rome, at home.

“We built the space together, and little Rome was born here,” Mr. Gentry said. “That’s kind of amazing.”

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