One modular roof building of 29° roof pitch was tested to investigate wind pressure distribution during thunderstorms. In order to get a comparison between thunderstorm induced and non-thunderstrom induced pressured distribution over the building, wall pressures, roof and internal pressures under those two different conditions was collected. The test structure was located along the west runway of Reese Technology Center adjacent to the WISE field laboratory. In this study, the results of field site data collection of thunderstorms and wind velocity spectra have been reported. The data collection was done in the summer of 2003. The longitudinal wind spectrum generally agrees well with the spectra of Tieleman. The lateral wind spectrum kind of differs from the spectra of Tieleman. The occurrence of thunderstorm has huge impact on the internal pressures and cavity pressures, which may determine the structural behaviour of building.