Many do-it-yourselfers know the joy of poring over house-plan books. Part frugality and part hobby, the process provides infinite hours of enjoyment studying the placement of staircases and laundry rooms, and debating the need for formal dining rooms or soaking tubs in the master bath.

The Internet has elevated house-plan ogling to a science, with hundreds of sites offering tens of thousands of plans, searchable by square footage, foundation type, number of bedrooms, baths and garage bays, architectural style, lot size and much more.

When it's time to move past the daydream phase into actually buying plans, there are a few things buyers need to know. The first is that they can't be returned, so you need to be ready to buy when you click the "order" button.

First, learn the rules
Before you spend hundreds of dollars on a set of stock plans, make a trip to your local city or county building department. Ask if they'll issue a building permit from stock plans or if you need a seal from a local architect. You also need to know if they'll allow you to make minor changes to the plans in the field or if the house must be built exactly as the plans are drawn.

In addition, you need to find out about easements and setback requirements on your lot. Easements are rights of way provided to the government for sidewalks or other improvements, or to utility companies for power, water or other services. Setbacks dictate how much space you need to leave around the edges of your property.

Unfortunately, this is the step that people skip far too often, says Linda Reimer, president of Design Basics, a stock house-plan provider.

"They fall in love with a plan," she says. "It's such an emotional thing. Then they call us back and say it won't fit on their lot."

It's also important to understand exactly what you're buying. Many people think they're paying for a stack of papers that show various segments of the house's construction, including the framing, the electrical system and the plumbing. You get the stack of papers, all right, but you're actually buying a construction license to build the copyrighted plan and the right to modify it.

Stock plans can cut costs
Dan Ramsey, author of The Complete Idiot's Guide to Building Your Own Home, says that buying stock plans can dramatically cut the cost of designing your own home. An architect may charge 2 percent to 3 percent of the project's value for a full set of plans -- that's $5,000 to $7,500 for a $250,000 house. Stock plans typically can be ordered for as little as $300, with the average running between $500 and $1,000.

"Some will reflect your local building codes, while others will be based on standardized codes for your region," Ramsey says. "You also can purchase enhancements that include suggested landscaping and decking."

Not all stock plan services are created equally. Ramsey recommends asking for a free or low-cost sample package that you can take to a local builder or architect for an opinion on the quality of the design.

"The right stock plans can save you thousands of dollars," he says. "The wrong ones can waste thousands in building costs."

Is off-the-shelf for you?
That's pretty much the experience that Pete Catalano of Lafayette, La., had when he and his fiancee wanted to build their own home.

"We wanted to buy house plans online because there were a lot of unique things we wanted to have in the house," he says. "We like to entertain a lot and we wanted a keeping room. We were also very much on a budget. The easiest thing is to go to an architect to design a house, but it's also the most expensive."