If you building a brick wood-fired oven, then caution is required in designing the door to minimize the risk of catching fire as well as avoid outside heat by the door heating up. To achieve this, the door needs to be insulated properly. One of the ways is to have a metal cover on the inside of the door and a wood cover on the outside. Between the metal and the wood covers, an insulating material e.g. perlite or ceramic fiber blanket, is filled to prevent direct contact between the inner metal surface and the outer wooden surface.
Further information: How to build a pizza oven