"I felt that the scope of work was manageable enough," said Ms. Siegler, 45, a former motion picture marketing executive whose checklist for remodeling her home in Malibu Beach, Calif., a few years ago included updating the countertops and light fixtures, painting, replacing the deck and deck framing, and a little interior and exterior decoration.

Lesson No. 1 for Ms. Siegler: do not go to gravel yards in your Manolo Blahniks.
Lesson No. 2: when you pick out a carpet, the carpenter really needs to know how thick it is.
"Somebody had to take all the doors off and shave them down because they wouldn't close," she said recently. "How did I not know that?"

And how did she not realize the implication of her decision to keep the original bathroom countertop, then add a moisture barrier and a layer of new tile? "It was much thicker, which meant that the stems for connecting the plumbing fixtures wouldn't fit." And so on and so on.

Acting as your own contractor — hiring the workers, setting a schedule and a budget, buying the materials and approving the work — appeals to some second-home owners. And there is a certain logic to it. After all, these weekend warriors are unlikely to feel the same sense of urgency they would toward a primary residence, so they can afford to take their time and handle building projects in bite-size pieces.

Skeptics, however, say the do-it-yourself contractor is like the lawyer who represents himself in court: he has a fool for a client.

"People think they will save a lot of money," said Ed Del Grande, himself a general contractor and the host of "Warehouse Warriors" on the Do It Yourself cable television network. "It can end up costing them a lot of money. If there are mistakes, there's no one else to blame. You have to keep in mind that the buck stops with you."

The foolish dreams of would-be contractors extend beyond the notion of extra dollars in the bank.

"I think it's not uncommon for people to underestimate the effort involved," said Eric Linthicum, an owner of Linthicum Custom Builders in Scottsdale, Ariz. "But I think that people need to be aware of all the complexities."

Not the least of which is corralling the subcontractors in the first place.

Ms. Siegler has been there. "They know they have no future with you as they do with a full-time general contractor, so it's difficult to get their attention," she said. "It's not that they'll do bad work, but they might not show up for the job."

Mr. Del Grande agreed. "You can sometimes end up just going through the phone book," he said. "If they're available it may be because they're not so good."

And would you know from good? What do you want to see from your drywall man?

What's the difference between skim coat and prep coat? If a subcontractor says, "Don't worry, we can fix that with a little caulking," should you worry?

To your worry list, add scheduling, as in figuring how much time the carpenters need to do the framing before the electricians and plumbers arrive (or do the plumbers come first?).

Since it's a weekend home, and therefore probably some distance out of town, would-be contractors need extra time to travel and supervise. And they need to make sure that they're adequately covered for liability, theft and damage claims, and that their subcontractors are licensed and insured.

There is also, as Ms. Siegler has found, an irrefutable law of construction physics to contend with: For every action there is an equal and opposite and expensive reaction.

Just ask Marty Hollander, the vice president for marketing at MeetingPlace, a voice and Web conferencing center based in Santa Clara, Calif.

He had a simple project on the table: replacing 14 windows and five glass sliding doors at his weekend home in Santa Cruz, Calif. He hired workers to help him, and soon the problems started.

"In doing the replacements I found that the people who did the work originally hadn't done any waterproofing," he recalled. "So we had to take out beams and parts of walls."

Then it turned out that the beams supporting a second-floor patio were rotting. Suddenly, Mr. Hollander, 49, was supervising carpenters and stucco and tile subcontractors.

Stephen Wald, 45, a Manhattan real estate broker who is building a 3,600-square-foot Mediterranean stucco house on Long Island, in the Hamptons, hedged his bets a bit by deputizing his builder as foreman. Still, he said, he has "nine toes in the water as contractor," hiring all the subcontractors, dickering fiercely with them and subsequently nipping 5 to 10 percent off each bid.

He's also on the site once a week, and bought all the materials for the house, from flooring to faucets, not necessarily a wise move, according to Mr. Del Grande.

"You should always have your subcontractors buy the material, because then they'll warranty it," he said. "If you buy it, you're responsible for any problems or repairs."

According to Mr. Del Grande, amateur contractors tend to be well organized and enjoy being in a position of authority, and would rather play a baseball game than watch one.

"These are very good qualities," Mr. Del Grande said, "but if you don't have the horsepower to back it up you're going to make a mess."

In fact, most people who cast themselves in the role have reason to believe that they can cut the mustard, or in this case, the miter.

Mr. Hollander, for example, once owned a chain of clothing stores whose construction he had supervised.

Susan Yungbluth, 60, an antiques dealer with homes in Vienna and on Long Island, said she was perfectly at home taking her cottage in Easthampton, N.Y., down to the studs because of her background as a dress designer, her experience in art restoration and her knowledge of architecture.

"I stood right out in the mud with the crew," Ms. Yungbluth said. "I watched every screw go in, every piece of molding. I think I got better work being my own contractor."

Ms. Siegler is ready to get back on the ladder again, and not only because being her own contractor halved her renovation cost.

"I'm eager to prove I wouldn't make the same mistakes again," she said. "It's kind of 'me against the toolbox.' I'm not going to let a little spackle get the best of me."