The energy storage is the main issue for an electric bus operating in the metropolis such as Bangkok. In order to provide a service of at least 200 km per charge and provide enough energy for air condition in bad traffic conditions, the batteries must be installed as many as possible on the bus. However due to an increased awareness to cater for disabled and elderly customers, a low-floor bus concept has been introduced in Thailand. As a result, an installation space in a lower area of the chassis was replaced with passenger seats. Therefore, remaining space for battery pack installation could be inside the passenger room and on the roof. However, the passenger room space would likely be reserved for more seat capacity. An installation of the battery packs on the roof was considered in this study. Such design could be considered unconventional especially in Thailand where such space would normally accommodate only the air condition unit. One of the main concerns would be passenger welfare i.e. whether the roof could bear an additional weight from the battery packs. Therefore, a structural strength of a roof structure of a 12-metre bus was investigated in this study. Two types of element were considered i.e. beam and shell. The former was utilised to determine the overall structural behaviour under the roof top loading. On the other hand, the latter was used to examine in details how the battery packs could be installed onto the roof structure. A static structural analysis was carried out to predict a structural strength under various typical driving situations, such as braking, cornering, where in each case an external load was assigned as acceleration acting on the battery packs in an appropriated direction. The simulation results consisted of stresses and directional deformations on the members of body structure. The results obtained from this study could be used as a design guideline for local bus manufacturers and operators interested in electrified city bus applications in Thailand.