If the source of heat for your oven is wood, you will need an oven thermometer to measure the temperature of the oven once the wood has been removed. If you want to cook a pizza, you will have to fire the oven for a long time so that the temperatures may rise since cooking pizzas require high levels of heat energy. Once you have fired your oven enough,read the figures displayed on the oven thermometer and get the temperature. With the figures you see, you will decide whether to start the cooking or not.
The material you choose to use in building your oven will determine the duration of time that the oven will continue to be hot. Therefore, make a wise decision on which materials for your oven. Generally, most people use fire bricks or cob.