A new approach for analysis of roof system due to the effect of explosion in confined explosion structures for the missile workshops. This paper discussed a new method for estimation of the behavior and required weight of roof for the confined explosion structures. The behavior of explosion in confined explosion structures affected by different parameters such as reflected pressure, duration of reflected pressure, gas pressure and duration of gas pressure. The main idea for these types of structures that will use as the missile rehabilitation workshops is to protect and creating life safety for the other parts of the workshop. The roof of this structure should fly after an explosion to decrease the gas pressure. On the other hand, this will be a weak point during an attack. In this case, these types of roofs could not resist against any strike. This paper discussed a mathematical modeling for the roof behavior. Finally the paper shows the new method for fabrication of these roofs without a frangible behavior considering the vent opening function. The known behavior of roof and designed mechanism for it could help the workshop structure to be protected by another shelter structure to present of any strikes.