Alcoves were once a prime way to add character. But these days, alas, they're just too expensive.

The average house comes with straight exterior walls, and fancy extras must be invented from within. Don't despair. There are ways to create alcoves. An extra closet, for example, can be ripped out, creating just about the right space for a bed or a built-in window seat. If you need an extra closet, you can build one or two on either end of a wall and create an alcove between them.

Or you can carve an alcove out of a gable. For a teen-ager who desperately wanted an alcove for her bed, I dropped a soffit down from the gabled niche around an attic window, joining it to the wall and creating an alcove for a twin bed. The little attic window actually looks attractive with a thick shelf under it for a nighttable by the bed.

To make the alcove a focal point I painted the walls apple green to match the carpet, and painted the alcove glossy white. The white base for the bed, the white bureau and the Japanese lantern stand out crisply against the green walls and quilted corduroy bed cover. On a thick white rod across the alcove, wall to wall, I hung a drapery of the green corduroy; a flick of the drapery and an unmade bed's hidden behind the green wall.

Even if you create the alcove yourself, and are missing a window, you can lighten the alcove space by adding a light strip or track on the ceiling or rear wall. This can be concealed behind a valance, the lights can be recessed in the ceiling, or you can let them show. A scenic enlargement of a photograph of the great outdoors can make a view unnecessary.

You can paint the outdoors on the walls of the alcove. I painted a big apple tree on the walls of a sleeping alcove for a young child who loved trees. The leaves, branches and fruit cover the entire space; the spread is made of green towelling, to look like grass, appliqued with three oversized red apples.

You also can create the effect of an alcove by setting the bed against the wall and building a four-poster bed of 4-by-4 stock lumber. Set thick curtain rods on the two short sides of the bed between the posts and one long one on the front, and hang sheets to match the bed. These can be kept closed on two sides, and open at the front, tied back with ribbons to match the pattern.

I enhanced this make-believe alcove idea by using white modular chests of drawers on either side of the four-poster, giving a built-in effect. The entire scheme, four-poster and bureaus, is totally portable.