Jeff and Yolanda Hittelman had outgrown their two-bedroom, 1,400-square-fot home. They needed a master bedroom -- larger than the 12-by-12 they'd been cramped into for some years -- away from their two small children. The Hittelmans also dreamt of a larger den, big enough to include a dining area; more closets and storage space; two new baths; a combination family and studio room; redwood decks off the master bedroom; and insulation for the entire house, which was designed in the 1950s and had none.

Then they stopped dreaming and became one of the growing number of do it-yourself homebuilders. The 1,500 square-foot, two-story addition Jeff Hittelman has just completed doubles the size of the home and increases its value to about $350,000. It took a year's time, but the total expenditute -- quality materials and labor -- was under $60,000. Hittelman figures a contractor would have charged twice that.

Hittelman's learned how to do the job himself at the Owner Builder Center camp near Nevada City, Calif., in the Sierra mountains. In three weeks, through a program of classroom instruction and hands-on participation in constructing a house, he learned every aspect of the home-building process.

The home-building camp is the summer residence program of the Owner Builder Center (OBC) in Berkeley, which offers year-round evening classes in nine locations in Northern California. A nonprofit organization, OBC was started in 1978 by Robert Roskind, 34, a former substitute high school teacher who spent 10 years building custom homes in North Carolina, and Blair Abee, 31, an experienced electrician who acts as business manager and codirector. A third cofounder, Charles Huddleston, was a general contractor and builder in Marin County. He is not the center's chief consultant and teaches OBC's local weekend seminars.

In less than three years, the OBC has become the largest of the how-to schools popping up from Maine to ycalifornia; more than 4,000 students have completed courses since its inception. The OBC summer program has 10 staff members, and the center has six full-time and 30 part-time instructors in Berkeley. Twelve organizations with OBC-trained staff are operating in nine states. This comprises half the building schools in the country, and more are planned.

Theere are two- and three-week OBC resident house-building programs -- five sessions of no more than 48 people each through Sept. 5. Roskind keeps the groups small to assure individual attention; the ratio of students to instructors is about 6 or 7 to 1.

The allure is high quality, affordable housing, and the basic lesson is, that savings increase with owners' participation. OBC graduates who have served as their own general contractors have saved an estimated 20 percent; those who have done just the finishing have saved from 30 to 45 percent; and owner-builders ambitious enough to have taken on the design, building and finishing have saved between 50 and 60 percent.

For example, the $100,000 home:

Can cost $80,000, if you know what you want, design the home and act as your own general contractor.

Can cost $56,000, if you have the foundation laid, the walls and roof framed, the siding and roofing applied, then take over the plumbing, electrical and finishing work yourself.

Can cost between $40,000 and $50,000, if you do everything from start to finish.

However, Jeff Hittelman cautions that inflation can distort an estimate, and says, "If you're smart, you'll doublie [it]."

Bill Loretta, an assistant high school principal who went to a three-week session with his wife Marie, is sold on tehg center's approach. "I grade them excellent," Loretta said. "Their hands-on program is fantastic. I'd love to apply what they do to education in our public schools! Yes, we plan to build. That's why we took the course. And we did nothing but learn."

But Darius Guernsey, who signed up for three weeks, dropped out five days early. "It was a lot tougher than I thought," he admits. And the youngest of last year's campers, 18-year-old Brett French, had just graduated from high school and thought he wanted to get into general contracting. "But I found out I was afraid of heights." French says. "My goal now is landscape architecture. The camp was a wonderful experience, though."

The campus includes cabins for couples, cabins for families, dining facilities, classrooms, playing fields, creeks and a lake. These who pitch a tent pay only $15 a week for the space and utilities, compared with cabin prices of $50 a week, per person.

Meals are $60 a week per person, but couples get a break on the tutition -- a two-week session is $400 for a single person, but only $600 for a couple. Not only are children welcome, but a child-care service is available.

Each day alternates between classroom situations and hard-hat work out on the job site -- laying foundations, sinking nails, using a saw. There's a schedule, and bells ring for classes, but it's not that rigid. It something exciting is happening on the construction project, nobody goes to class that day. Evenings include free time, social events, or additional classes.

The curriculum covers everything from preparing a piece of ground to finishing a roof, and participants learn each stage in detail. They study foundations, flooring, plumbing, electrical work, framing, siding, roffing, insulation, tiling and finishing. Each subject, including codes and permits, an important preconstruction phase, is taught by experts. This summer's staff features a cabinet maker, a tile setter and an electrician, as well as professional contractors and carpenters.

The classes are geared to the novice and stress how to avoid common mistakes. Clear, simple texts written by the staff are used in eac course.

Women comprise almost a third of the OBC camp students (35 percent of the owner-builders across the country are women).

"The information and the skills aren't the hard part," says center director Roskind. "Building is just a sequence of simple, logical steps that one has to plan, time-line and manage. But it's a demanding, long-range task, and it takes perserverance. If you've got a full-time job, you're looking at five years of weekends."

(For information about the summer home-building camp, write: Owner Builder Center, 1824 Fourth St., Berkeley, Calif. 94710, or call their toll-free, 24-hour number: (800) 547-5995).