The rule of thumb is that they should be at least 27.5 inches tall and the width and length should be about 25 percent larger than your dog's nose to flank length. Most standard dog houses are spacious enough for a large German shepherd, but it never hurts to have a small dog in a big dog house either. However, for companies that sell dog houses in different sizes, you can sometimes save money by sizing down. Make sure to look at all the product photos and customer review photos of a dog house to get a better perspective of how big the dog house you're interested in really is.