Path loss Propagation models plays a fundamental role in planning and designing of mobile radio communication link. In this paper a building penetration path loss model was developed using AUTOCAD. The model involved the combination of three mechanisms of signal propagation; refraction, reflection and diffraction. The signal penetration through building wall was modelled as refraction using Fresnel Refraction Coefficient and the signal propagation through the roof was modelled as diffraction using the principle of knife-edge diffraction. The developed building penetration path loss model was compared with some empirical path loss models namely, Log distance path loss, Okumura, HATA and COST-231 models and the results showed that the models compared accurately with the existing path loss models. Hence, it can be stated that the developed building penetration path loss model can be used to accurately predict signal attenuation in buildings located in an urban environment.