Select a location. If you're in a house with a basement, call dibs on the basement as the site of your man cave. If you lack a basement, then find a room you can commandeer as your own.
Choose a decorating style. Outfit your man cave with decor that suits your tastes. If you're a sports fan, array your man cave in your favorite team's colors. Hang up jerseys and posters of favorite players and put team helmets on display. If you're a movie fan, create a theater-like atmosphere by buying dark shades to cover the windows and putting up posters of your favorite films. Bring all those odd collections out of storage such as hat collections, beer mugs, bottle tops and old comic books, and create a little museum in your man cave.
Select essential items. By definition, a man cave must house things most men can't live without such as a television -- preferably a flat-panel -- video-games, a big comfortable sofa or enough bean bags to seat your friends when they come over to hang out and watch the game. If you don't have enough furniture and your budget is tight, get creative and use old storage boxes as makeshift chairs. The one item you must have is a refrigerator, either a full-size or a mini-fridge, or at the very least a big cooler filled with ice.
Stock the man cave with snack items, beer, soda, candy and other favorite foods. Make sure you have action and comedy DVDs and plenty of video-games for hours of uninterrupted enjoyment.