Although Building Information Modeling (BIM) has been around for over five decades, its integration with Big Data generated by IoT networks has raised research interest. This fusion enables the Digital Twin of a Building (DTB), a real-time virtual replica facilitating efficient location-based services, precise monitoring, and enhanced operational efficiency. Despite its alignment with the Smart City paradigm, widespread adoption is hindered by the initial investment for IoT network deployment. This article presents a comprehensive process, from optimizing IoT network deployment to implementing robust location-based services. A genetic algorithm leveraging the BIM database improves coverage by 44% compared to random deployments, while a multi-tier architecture based on deployed and roaming users’ devices extends service availability to 80% of devices without internet access, enhancing overall service quality by ∼200%. Eventually, the versatility of DTB is showcased through the use case of indoor guidance services, concluding with potential research directions using the DTB.