So the last child has gone off to work or marriage or college and you've finally dried your tears.

Time to take a look around the old homestead. Big, isn't it?

And weird, too, with all the kids' stuff still around, in the living room and the coat closet and, of course, in their bedrooms.

You have come to a phase in life traversed by many parents before you: The Empty Nest. And with it, you have choices about what to do with the home you now own.

You could sell it and move into something smaller, just right for one or two. But what if the children want to visit for Thanksgiving? What if one of them moves back in? What if they finally give you grandkids? Where will everybody sleep?

You could keep the house exactly as it is, with their bedrooms like little shrines to their adolescent selves, dust accumulating on their trophies and ribbons.

Or you could take a path described in a new book geared to empty nesters, "The House to Ourselves: Reinventing Home Once the Kids Are Grown," by Todd Lawson, Tom Connor and Rob Karosis (Taunton, $35).

Lawson is an architect and Connor is a soon-to-be empty nester, and they spent a year studying how architects and homeowners revised family homes or built new ones to accommodate vibrant new lives.

The first surprise? Not everyone downsizes or moves to Florida.

"There's so many different approaches," Lawson said. "And the size thing was a surprise, in that people aren't necessarily going smaller. Some are, some aren't. Some are going bigger -- I guess they're spending their kids' inheritance!"

"The House to Ourselves" has photographs and floor plans of 20 homes designed and redesigned with couples in mind. Only one is in a retirement community. The rest are in resort areas or in the neighborhoods where the couples raised their families.

"The AARP did this survey, and 85 percent, I think, of the people in this age range want to stay in their homes as long as possible," Lawson said. "So, many of these homes were designed with long-term goals in mind."

Baby boomers, Lawson said, are driving a trend of creating empty-nest homes that don't resemble your grandmother's house, with its formal living room and array of bedrooms.

The boomers are building or remodeling houses to satisfy their own needs and accommodate their hobbies, he said.

For example, several of the houses in "The House to Ourselves" boast extensive new home offices for writing or consulting projects or simply getting away.

Another chapter shows how a North Carolina couple added 3,000 square feet to a 900-square-foot cabin. The new space includes an exercise room, a study for the husband and a circular weaving studio with a library loft for the wife.

What else do empty nesters want? Flexibility, Lawson said.

They want spaces that can be cozy for two yet comfortable for a crowd. And when they imagine places for family to stay, they want space that can be closed off to cut down on daily maintenance, or transformed into something they use every day.

For many of the homes in "The House to Ourselves," the sleepover space is not a mere guest bedroom. A house in Seaside, Fla., tucks sleeping lofts, reached by ladders, into the corners of a two-story great room. The lofts make fun spaces for the grandchildren to sleep but don't eat into the day-to-day floor space.

Other couples design an open floor plan that can be closed off as needed. An apartment in Davis, Calif., for instance, features rolling barn doors made of steel and glass. They can close one end of the living room off to create a guest room -- or open up to make room for the Thanksgiving dinner table.

Some couples elect to create a family compound by building a separate guest house on their property. The owners of a Rhode Island cottage created a two-story tower with bedrooms and baths and linked it to the main house with a covered breezeway.

When the kids and grandkids leave, the couple can close the tower off and not worry about keeping it dusted and heated, Lawson said.

A separate guest apartment can be a great idea, Lawson said, for another reason: It can become a place for a live-in caretaker, should the homeowners ever need one.

Empty nesters fall into two categories when it comes to planning their retirement homes, Lawson said. Some want to be sure that they can always live in their new homes, so they plan for reduced vision, hearing and mobility. They put in wide doorways and halls; they take out thresholds and eschew steps.

And the rest don't want to think about the potential infirmities of age at all.

Lawson remembers a Brentwood, Calif., ranch owner who remodeled to create a dramatic living space three steps down from the rest of the house. Lawson asked the man whether he worried about not being able to navigate those steps in the future.

" 'Naw, I'll worry about it later,' " Lawson said the man told him. " 'I'll just roll up to the edge of the steps and yell for the crowd to follow.' "

What advice does Lawson have about planning for an empty nest -- even if the children are still at home?

First, consider putting a bedroom and bath on the same level as the kitchen and living space and the rest of the bedrooms on another level. You could use that first-floor bedroom as a guest room or study, if you don't want it for a master bedroom.

Later, when the children are grown, you can move downstairs and use the second floor as guest space that can be closed off when it isn't needed.

If you're building or remodeling, plan for wide halls and doorways throughout the main living space and future master bedroom, Lawson said. If your halls are five-feet wide, say, rather than the typical three feet, you can line them with bookshelves now. Later, should you need a walker or wheelchair to get around, you can take the shelves out to give yourself maneuvering space.

And if you're planning an office or workspace now, think about placing it away from the main living area and bedrooms, maybe over a garage or in a separate pavilion. Plumb the space for a full bath, and you'll be set to create a caretaker apartment should you ever need one.

Flexibility, again. Lawson hopes "The House to Ourselves" will get many families and couples to see their futures within the book's covers.

"The hope for the book is that someone who's getting ready to do this and doesn't really know what to do will open it up and say, 'That's me. That's us!' " Lawson said.