Back when bathrooms were seen solely as functional rooms, remodeling and redecorating were relatively simple. You bought new fixtures if necessary - and if you chose a color for them, that was pretty adventurous - or you freshened up the look with a change of paint or wallpaper. A major overhaul meant more money and decisions, but most of those decisions were driven by practical considerations - like which materials and products were easiest to clean.

Enter the current era of the bath as a retreat for relaxation, in which a spa-sized tub (preferably with whirlpool action) is the norm in most model homes and builder's plans and in all the shelter magazines. Increasingly, upscale baths also include exercise equipment, so you can work off the stress of a tough day and then relax."A bathroom is more than a bathroom now - it's an extension of your lifestyle," says designer Robert Lewcock of Zimmerman Design Group in Wauwatosa, Wisc.

If you want to create a bath/retreat in your home, the decisions can seem endless.

Where to start? It often helps to take cues from the experts, people who design for a living.

Four designers who have created new model bathrooms at the Kohler Design Center all followed the same basic steps in planning their rooms and offered advice that can be used in remodeling at any price point.

While their work ranged from lean and minimalist to traditional and clubby, all of them started with an overall theme, all based their plans on the personality and needs of a client and all used one or two key elements as starting points.

In some cases, these elements were established by Kohler; in others, they were chosen by the designers.

Benjamin Noriega-Ortiz, a New York City designer, created a Caribbean bathroom based on the colors of the sea surrounding his native Puerto Rico. "These are the colors of the water where I come from," he says, as he points out three shades of blue (called cobalt, seafoam and skylight) in ceramic tiles used on an undulating, wavelike wall.

He worked from a "given" established by Kohler, the use of fixtures in the company's "Fleur" line. It has curvaceous, anthropomorphic lines that Noriega-Ortiz admitted he initially disliked.

"I wouldn't have chosen it," he says as he points out the fluid lines of a sink, tub and toilet. But the shape of the fixtures eventually led him to follow through with the wave-like wall and perfectly fit his theme. "Now I like it. I would choose it," he says of "Fleur."

To help plan the room, called "Bathing in a Gentle Breeze," he created an imaginary client and a list of the client's preferences. (He envisioned a couple, a sculptor married to a dancer, with two children ages 5 and 6.)

Because he wanted the bathroom to appear larger, he chose the smallest size sinks available in the fixture line. "That's a way you can trick people into thinking the room is bigger," he says. "Your readers can do that."

To the same end of stretching the space, he chose hard, reflective surfaces for the walls and floor. "Unconsciously, it reminds people of a mirror," he says. The shiny floor, made of concrete coated with an epoxy finish, gave the room the "wet look" he wanted.

Texture, rather than color, got the nod in the sophisticated mono-chromatic bathroom planned by the Atlanta design team of Charles Gandy and William Peace. The hues are parchment-on-parchment-on-parchment and the restrained use of color creates a tranquil place where users rank foremost, Gandy says.

Their envisioned client is an urban, athletically inclined working couple with no children, Gandy says. Both husband and wife are career-driven, "cutting-edge" people who are stressed out enough to make a punching bag and boxing gloves the most logical piece of exercise equipment in the room. Hence, the theme, "The Main Event."

The pair are also no-clutter people who want "a place for everything and everything in its place," Gandy says. And because this busy couple has little time for conversation, the designers included a comfortable banquette for spur-of-the-moment discussions.

The spare look emerges from the designers' approach. "One of our dictums," says Gandy, "is to simplify, then exaggerate."

The idea is best illustrated by a lengthy, wedge-shaped limestone counter that cants out into the room like a piece of sculpture. "We simplified the limestone and then really used it," Gandy says.

Lewcock put a different spin on elegance in his handsome bathroom called "A Gentleman's Retreat."

Kohler had two requests of Lewcock: that he use a classically styled line of fixtures called "Memoirs" and that he choose one of two design themes, art deco or a traditional men's club look. Lewcock chose the latter and then picked two elements - a tile design and an upholstery design - as foundations for his plan.

The tile, the "Enchanted Forest" line from Ann Sacks Tile & Stone, features sculptural images from the forest: a mouse, crow, quail, rabbit, doe and an oak leaf.

The upholstery on a Milling Road chair mirrored the forest theme and suggested a palette of burnt orange, muted sages and putty.

The rest of the room - from its cherry woodwork to art glass with animal images to murals with a forest theme - flowed from Lew-cock's initial choices.

Lewcock stressed the advantages and adaptability of working with a theme in remodeling and re-decorating. Bathrooms, he says, "shouldn't be a cold, institutional space but should reflect things you like to see and do."

While the enchanted forest theme appealed personally to him, Lewcock notes that the same bathroom plan would work well with other themes, such as equestrian or racing-car themes.

Vonda Tomlinson, a design supervisor at Kohler, expresses a similar theme in beiges and blacks. To heighten the challenge of creating her bathroom, called "Back to Nature," she decided to use recycled materials as much as possible.

Predominant in her use of these materials is flooring of reclaimed maple and a wall of old Cream City bricks. She introduced water images with tiles decorated with ancient Greek wave designs and used curving lines to echo the "Folio" bath fixtures she was required to use.