House plans with a den offer flexible space in the home for a cozy living area, home theater, game room, or play space for children. A den can serve many different purposes, and a common purpose would be a smaller and more intimate living space. Comfortable furniture and entertainment, such as games or movies, make this a place where individuals or smaller groups can enjoy downtime. While the great room or living room is more formal and intended for entertaining, the den or family room is a casual space that is small and cozy.