In this study, we analyze the field distribution in large buildings using Winprop, a commercial 3D simulation tool based on ray tracing. Furthermore, we analyze the shielding characteristics and selection of optimal reception points by comparing them with the probabilistic algorithm PEPWB and numerical analysis methods. To accurately interpret the shielding characteristics of large buildings, it is important to determine a receiving point that indicates the representative values inside the target space. Inside a building, resonance may occur because of the reflection, transmission, diffraction, and scattering characteristics of the radio waves, resulting in a low or high reception power at a specific point. Therefore, by analyzing the internal field distribution, it is possible to select an appropriate receiving area to interpret the shielding characteristics in an actual measurement environment.