We hadn't been inside the West Virginia cabin for more than 15 minutes when my friend Jane pulled out a tape measure. OK, the place was about 16 feet wide. Length? Two 25-foot lengths plus the hallway and then the bedroom for a total of 64 feet. A wide deck ran the length of the open-plan living-dining- kitchen, offering views of green, green, green. Inside and out, the place was modern.

The cabin was prefab, and Jane has a nice lot looking onto Chesapeake Bay. It's topped by her childhood summer cabin. But wouldn't it be nice, she wondered, to replace it, or augment it, with a modern prefab structure?

Prefab is simply a system for building a regular house, of almost any style, in modules or panels in a factory. With modular houses, there's a lot of extra engineering involved: After all, at the factory and at the home site, pieces of the structure have to be picked up by a crane and set in place, first on the delivery rig and then on a concrete foundation — and in between, they bounce around for miles on a truck. With panelized construction, sections of walls, complete with innards such as electrical wires, are stacked on trucks, then linked together on site. When finished, prefabs look like regular houses.

There is a wide spectrum of prefab houses and the companies that make them.

At one end are factories that spit out econoboxes that, despite superior engineering, can resemble shipping containers. They include the one-bedroom, one-bath, "i-house" by Tennessee-based Clayton Homes. With upgraded flooring and appliances, it's about $85,000, including delivery, or about $117 a square foot. ECO-Cottages by Nationwide Homes of Martinsville, Va., offers a 513-square-foot, one-bedroom, one-bath cottage starting at $59,500, or $116 a square foot. (Prefab prices do not include the cost of the land or foundation, or site-prep work.)

At the other end of the cost spectrum, California-based LivingHomes offers high-style contemporary designs at square-foot costs that range from $220 to $250, and much more for custom designs. That doesn't include design fees. What you're getting, the company says, is a soaring architect-designed house — steel frame, lots of glass — for 20 percent to 40 percent less than a similar site-built house.

Compare these numbers with a 2,200-square-foot house offered by Ryan Homes in Clinton, Md. — $121 a square foot, including the land it sits on — and the decision to go prefab is not clear-cut.

The cabin we were visiting belongs to Chris Brown and his wife, Sarah Johnson. During construction of their cabin, called Lost River Modern, Brown kept a blog, including his estimates of what he thought things would cost and the real cost.

Jane and I looked over the blog. When we saw the staggering $356,000 total for the nice two-story, three-bedroom, two-bathroom, 2,048-square-foot house in far-out West Virginia, Jane began revising her expansion fantasy.

The cabin is part of a mini-slice of the prefab world: stylish, higher-end houses designed by architects interested in homes that are built to be more labor- and energy- efficient and less wasteful than site-built houses.

Brown and Johnson were thinking about a getaway house they could rent out when they saw the winner of the 2003 Dwell Magazine competition to create an innovative prefab house for $200,000 — an effort to stoke the fire under prefab, which always threatens to peter out in the face of market realities.

The winner was Resolution: 4 Architecture of New York, and Brown approached principal architect Joe Tanney in 2006. Some prefab designers think in terms of cubes and at least one thinks in triangles, but Res4 thinks about "bars" — long or short sections that can be stacked or angled or cantilevered to achieve interesting effects.

Designing a prefab house requires access to a factory that can create it. Mass-production factories are not disposed to interrupting their assembly line for a small project.

Contemporary design has another challenge: The architect or owner has to find a modular construction company that is attentive to finishes.

An advantage of prefab is supposed to be time savings. But with the tweaking of machinery and refining of designs, Brown estimates the house was "in the factory" for a year.

Another year was spent after delivery, finishing some complicated flashing for the Charles Goodman-style "butterfly" roof and the interior, with Brown and his brother-in-law providing a lot of the labor. (They also applied the exterior cedar siding and built the deck, then built the staircase and tiled the bathroom.) Brown, a graduate student in English literature, said the "real advantage" was that he and Johnson, a nurse, "didn't have to manage a building site" that was almost three hours from their home in suburban Washington.

Without the land, excavation or $12,000 for the road up their hill, Brown and Johnson calculate their square-foot cost as $150 to $160, "the low end of prefab," he said. At least of "architect prefab."