(FORTUNE Magazine) – "You simply can't build a $20 million mansion that doesn't have a wine cellar!" declares Jeff Smith, a wine consultant based in Beverly Hills. He's not joking: One client who recently retained his services is in AA but wanted a lavish cellar to impress guests. Smith's company, Carte du Vin, works with around 100 CEOs, magnates, and Hollywood executives, doing everything from overseeing the creation of a custom cellar to tracking down rare bottles at auction and taking inventory of vast collections. Smith can easily spend $90,000 filling a client's cellar, but for those on a slightly more limited budget, here's his primer on what every collector should know.

GET A ROOM Ask a contractor to insulate the room and put in a vapor barrier. The magic number is 55 degrees for a wine, but consistency is just as important--lock in a temperature somewhere between 53 and 59, and you'll be fine. Humidity should be around 60% or 70%. I like the WhisperKool refrigeration units (up to $2,244). And don't even think about having a dinner party in your cellar: It'll ruin the wine if you warm up the room for the night.

INVEST FOR LATER Start with the first growths from Bordeaux: Château Lafite, Mouton, Latour, Haut Brion, and Margaux. The biggest of the big boys is Domaine de la Romanée-Conti. Every year it offers a small number of mixed cases for $5,000 to $8,000. Buy that, and it shows you're a real player. The hottest California wines are Harlan, Colgin, and Screaming Eagle. They're exclusively sold to a mailing list, but you can also find them at auction.

RACK 'EM UP Use rope lighting, which is insulated and won't warm the room. I like racks that display a bottle at each level, rather than diamond racks, which are harder to maneuver. And don't bother with fancy wine software: An Excel spreadsheet with ideal "drink by" dates (available on winespectator.com) for each bottle is all you need.

ACCESSORIZE The best glasses are the Riedel Vinum series in Bordeaux, Burgundy, and chablis shapes, and the dessert wine glass (www.riedel.com/website/english). Spiegelau, which was recently bought by Riedel, sells sturdier, less expensive versions. For corkscrews, at home I'll use the Italian Vigneto deluxe cork extractor; on the road I travel with my shell-handle Laguiole corkscrew. I decant almost everything with a Baccarat Dom Pérignon wine decanter. It was a wedding gift.

DRINK IT NOW For a dinner party, you can't do better than a Châteauneuf du Pape, which is tremendously undervalued. With Chinese takeout, I'd try a light and sweet wine like Domaine Zind Humbrecht's pinot gris, the Clos Windsbuhl, or a Huet Vouvray (about $50). For an inexpensive holiday champagne, try a Nicholas Feuillatte--a nonvintage rosé. It's only $35. If you're splurging on a red, go for the 1982 Latour ($700 to $900). That's what 100 points on Robert Parker's scale tastes like.