A photograph of a model vacation house at The Woods development that accompanied a story in the June 17 Real Estate section described the model as being bare inside. The house shown was sold with a finished interior, including carpeting, kitchen appliances, and a septic system, according to the developer.

If you're enticed by ads for inexpensive mountain cabins an hour or two west of town, but haven't really checked the market, the terms can be confusing. What do yo get when you buy a cabin shell? A shell with utilities? A finished cabin?

The differences can be considerable, both in price and usefulness to the owner.

The basic shell, available through developers on their lots or through building companies on yours, is typically a frame cabin set on posts to accomodate a sloping site. Inside there are usually no room partitions. (You put these up yourself if you want them.)

The walls are uninsulated and unfinished. There is no electricity, no sewage system, no water supply. The shell is essentially a wooden tent.

The idea is to provide a low-cost starter home for vacationers. When purchased from a developer, the shell normally comes with a lot of three acres or more (often this is because of subdivision regulations), and it may be located on a tract with other recreational facilities, such as a swimming pool or lake, boat docks and tennis courts.

As a strictly warm-weather retreat for people who don't yearn for the amenities, or for the dedicated do-it-yourselfer, it may be a good investment.

The problem comes when the owner decides he wants more - a bathroom, for example. For this he needs a well, electricity to run the water pump, and a septic system. They are expensive, sometimes half the cost of the shell itself.

They can be hard to finance since they are not included in the mortgage on the property. Most important, they are difficult to have installed from Washington, particularly if the cabin is two hours or more away.

The owner must see to perc tests and permits. He must interview subcontractors get bids, and arrange for the work to be done.The operation is at best time-consuming, often aggravating.

Recognizing this, some developers now offer a shell that has the basic utilities included: water, spectic system and electricity. In large developments there is usually a central water system, which is more economical for both buyer and seller. Central water also means the developer can place his cabins on smaller lots, typically about one acre.

There are differences between developments in the extent of amenities offered. In some, electricity is brought only as far as the box to the house.

In others, shell are completely wired, including all outlets, switches, and hookup for electric range. Most builders provide a bathroom. Some include studding for interior room divisions. Some include a paved driveway.

Though the utilities are there, the shell-plus still needs a certain amount of work before it functions as a true vacation home. Most buyers want to put in at least a kitchen, insulation and paneling, and heat. Even this, done as a part-time project, can be a chore.

Jim and Pam Andre, a Capitol Hill couple who finished their West Virginia cabin several years ago, say they found both rewards and drawbacks.

"The biggest plus," says Pam, "is being able to create an absolutely unique environment. We looked at this 24 by 24 cabin and said, 'What are we going to do with it?' And we did it! We enjoyed doing our own handwork."

But it took a long time. The Andres finished their cabin over three summer seasons, working mostly on weekends. To avoid waiting for deliveries during working hours, they carted everything they could in their Pinto, including sheets of panelling bought in Hagerstown and tied precariously to its top for the trip down Interstate 81, over bumpy West Virginia two-laners, and finally on gravelled road to the cabin.

Today, some of the larger developers try to help out their buyers.

For the buyer, the important thing is to determine first exactly what amenities and services are included. How complete are electrical and septic systems. What are the fees for water? Will the developer provide materials lists and help you find reputable subcontractors and suppliers if you need them? Do he have a finish crew to do work you can't handle? How reasonable are his price?