How to Build an Earth / Clay Oven
In my definition then, a clay oven is any hollow, dome-shaped structure constructed out of clay, clay and sand or clay and straw, used for the purpose of baking and roasting food. It has a brick floor and usually a chimney.
Most traditional clay ovens are built outdoors and may or may not be covered with a simple roof structure. In a SHTF situation the gas might go out permanently and you may want to cook more how we are used to. You could always cook on a skillet over a fire but this is just another way of cooking to make sure you and you family have a form of cooking.