Children's rooms are generally "off limits" when guests are being shown through a house. And it's not usually because the children have requested it but that parents are too embarrassed to reveal the messy rooms.

Sometimes the problem of disorderly kids' rooms is the result of insufficient storage space for toys, games, puzzles, stuffed animals, school books and the multitude of other paraphernalia these kids manage to collect. And Western Wood Products Association (WWPA) has come to the rescue by coming up with some practical, do-it-yourself solutions that will restore order to a room.-WOODEN MODULES - These modules are easy to make. And like building blocks, they can be stacked in a variety of ways; they can be rearranged to become a pretend kitchen, store or whatever.

They can have shelves, doors, or be left open.

To make a module, simply edge glue two 1-by-8-inch boards for the sides, top and bottom. After the glue dries, cut the pieces to the desired length and join at the edges with six-penny finishing nails and glue.

For variety, use shapes other than rectangles. Cut out triangular and half-circle pieces for a child's chair, a doll house, or anything else your imaginative mind conjures up.

WWPA suggests that you use clear, close-grained grades of Douglas fir. They also recommend that you finish the modules in natural wood tones. But you might prefer to add occasional accents of color to add variety and visual excitement to the unit.

-BOOKSHELVES - Schoolchildren will enjoy bookcases of their own. And if you're a pretty good do-it-yourselfer, you'll find them easy to build. Just follow these steps:

l. Sketch a simple design. A standard size is 36 inches long and 36 inches high.

2. Allow about 10 inches of shelf space, since most books are about 9 inches high. If you have larger books, allow for 13 inches between the bottom and second shelf.

3. Select appropriate lumber, such as knotty grades of ponderosa pine. Or you might prefer the close-grained appearance of Douglas fir. These boards will take stains, paints or clear finishes well.

4. Cut the wood to lengths specified in your design.

5. Assemble using No. 10 1 1/2-inch flathead wood screws and glue. Although butt joints are the easiest to make at the corners, mitered corners give a finer appearance.

6. Countersink all screws so the heads are flush with or below the surface of the wood.

7. Sand the unit with fine sandpaper. Pick up any wood dust with a tack cloth or damp sponge. Apply coats of finish, rubbing lightly with fine steel wool between coats.

-WALL-TO-WALL BOOKCASE - As kids get older, they'll be bringing home piles of school things, and a small bookshelf will not be sufficient. You might need a wall-to-wall bookcase.

The one suggested by WWPA is low and easy to reach. And it takes up little floor space.

The WWPA suggests you use 1-by-12-inch boards. Follow basically the same steps mentioned in the previous project, except you add the following:

1. Install vertical dividers for added stability and visual appeal. To alter the pattern, you can stagger the dividers from one shelf to another.

2. For a more professional look, nail and glue 1-by-4-inch boards to the underside of the bookcase.

3. Leave four inches of space above the last shelf and top it with a small width board, such as a 1-by-6. This space is well-suited for smaller items.

For a free listing of other wood projects, write to Western Wood Products Association, Dept. HI-887, Yeon Building, 522 S.W. Fifth Ave., Portland OR 97204-2122. Step-by-step plans for the storage modules discussed above are available by sending 75 cents in coin to WWPA, Dept. P-162C, at the same address.