Insulation
Check the door's R-value. The R-value rating indicates how well the door resists heat flow, or provides insulation. A higher R-value means the door has better insulation. If you use your garage for a workshop, a washer and dryer area, or children's play area, you will need to be more concerned with your door's R-value. In these instances, a door with an R-value of 3 is recommended for moderate climates. In colder climates an exterior door with an R-value of 10 is recommended if the garage is used for everyday activities. Even if you only use your garage for parking cars or storing tools and outdoor equipment, you may want to consider buying a door with a higher R-value to help insulate your home and reduce monthly energy costs.

Style and Type
There are numerous styles of exterior doors to choose from. Your door should complement the style of your home. Exterior doors are made with flush panels, raised rectangular panels, and raised square panels. Look at the doors in your neighborhood and in other residential areas to get an idea of what style of door looks best with your style of house. Wooden exterior doors offer a wider selection of styles, but steel doors can also enhance the appearance of a home. Two specialty styles of wooden doors are the carriage door and barn door. Both of these doors look as if the two sides swing open, but they open like a conventional door. If price is a consideration, look at the available selection of steel garage doors, since these are generally less expensive than comparable wooden doors.

Color
Most doors are available in several different colors. Exterior doors usually match the trim color of the house, but your door can be any color you wish. Keep in mind that dark colors will absorb more heat, and a dark door may end up bowing after years in the sun. Use unconventional door colors with caution. Even though you think a color will look good and complement your home, non-traditional door colors may not be as appealing after some time. Check with the experts at your local home supply store if you need help deciding on a color for your door.

Quality
The saying, "You get what you pay for," applies to exterior doors. You want to make sure your door can withstand daily use and is strong enough to last for years. You do not need to buy the most expensive door to have a quality door, but spend what you can within your budget.