Many football fields in the NFL are oriented north to south so that players will not be hindered by sunlight, but there is not a rule that makes the fields run north to south. There are a few stadiums, such as the ATT stadium, that run east to west. The NFL has no official stance on whether stadiums should be oriented north to south or east to west.
When football stadiums are being designed and built for NFL teams, there are a lot of factors that go into the stadium's design. Depending on the location of the stadium, the type of team and the amount of fans the stadium will hold, architects must decide whether the stadium should have a roof or not, whether the field should be actual grass or artificial turf, and whether the field should have heating coils or be completely natural.
Similarly, the orientation of the field is vital to how the game will be played and viewed. Some argue that all fields should be oriented north and west so that the sun will not get in players' eyes. However, if the field is oriented north and south, then there are often full sections of seats where the sun will be in the eyes of the fans. There is no right or wrong way to orient a football field, but walls and materials are specifically placed such that the game will run smoothly and so that the fans can enjoy it.