These days, buying a private jet is easy; what’s complicated is furnishing it. Even the Sultan of Brunei can’t always get his way.

Several years ago, Leslie Jennings, an aviation designer based in Mead, Oklahoma, was given a $15 million budget to overhaul the interior of the sultan’s Boeing 747. Among the client’s requests was a crystal chandelier hanging over the dining table. But the fixture had to be completed in plebeian Plexiglas—not, of course, because the sultan couldn’t afford the real thing, but because Federal Aviation Administration regulations didn’t allow it.

“Chandeliers are fixtures that move around a lot and are potentially a safety issue,” says Eli Cotti, director of technical operations with the National Business Aviation Association. “But I’ve seen a chandelier on a DC-10, a high-end project in the entryway that retracted into the ceiling at takeoff and landing.”

Anyone who spends millions of dollars on an aircraft—a Gulfstream can cost between $13 million and $47 million, including outfitting the cabin—isn’t likely to want coach-class interior decoration. But trappings that don’t meet regulations, or are too troublesome to be worthwhile, require a little compromise.  (View chart.)

Private jets, unlike turnkey condos, don’t come presupplied with décor and amenities. Unfinished, or “green,” planes pass through completion centers, like those operated by Midcoast Aviation, in Saint Louis, where they are furnished, painted, and decorated. Some manufacturers, like Gulfstream, which has five completion centers, finish all of their own planes; Gulfstream even refurbishes those made by other companies. Other manufacturers, such as Midcoast Aviation, a preferred partner of Bombardier, outsource their finishing work.

Completion typically costs between $3.5 million and $12 million, says Ann Hein, director of marketing at Midcoast Aviation. But some clients are willing to pay far more for the interiors they desire. In 2003, Jennings was given a completion budget of $36 million for a head of state, whose plane, a Boeing 767, had to accommodate an entourage of 50 to 60.

No matter what the price tag, anyone planning to enter U.S. airspace has to answer to the F.A.A.—and the laws of physics. The agency has issued hundreds of aviation-safety advisory circulars detailing what is and is not allowed when it comes to the design and construction of airplanes. There is not, however, a single rule against adding a crystal chandelier to your plane, says Chris Carter, the F.A.A.’s manager of technical programs and continued airworthiness, aircraft certification service, in Washington, D.C. As far as the agency is concerned, the sky’s the limit for interior design—that is, as long as evacuation routes remain clear, flammable items are fire-resistant, electronics don’t interfere with navigational systems, and fixtures don’t pose any of a number of other hazards.

For owners who want everything from high-tech coffeemakers to interior doors between staterooms—solid doors are normally prohibited in favor of soft, curtain-like partitions—the long list of regulations means either lowering their expectations or undertaking a lengthy (between 90 and 120 days) exemption process, Carter says. An exemption isn’t granted unless the F.A.A. is convinced that the addition won’t be dangerous; in the case of the coffeemaker, the owner had to show that hot liquid wouldn’t splash onto passengers during turbulence.

As for the sultan, his splashiest amenity was an onboard Jacuzzi, which can be installed on large planes but is far from practical on smaller ones. “If you put in a swimming pool or bathtub, you immediately change the effect of the aircraft,” says Robert Baugniet, director of corporate communications at Gulfstream Aerospace. Additional water weight means less efficiency and more fuel consumption, although the effect is greater on small aircraft, like a Gulfstream, than a converted 747.

That’s just one reason Jacuzzis aren’t popular amenities at Gulfstream. Baugniet says his clients—including dozens of corporations, several governments, and a few wealthy individuals each year—are less interested in hot tubs than in whether laptops, fax machines and satellite telecommunications systems will work at 50,000 feet.

“Clients want high-speed data capabilities, high-definition flat-screen displays, and interfaces for their iPods,” says Hein. All of these, and more, are doable. But while private jets can be outfitted with screening rooms and beds, you might want to rethink megascreens in every corner or furniture made of solid mahogany, which tend to make your aircraft unnecessarily hefty.

“When designing an aircraft’s interior, you have to think in terms of trade-offs,” Hein says. “Every ounce of weight that’s added to the interior decreases the amount of weight that can be brought onboard, whether that be passengers or your company’s products.”