Accessory Dwelling Units (ADUs) are increasingly recognized as a solution to the housing shortage, with the market for modular and prefabricated homes expected to reach $300 billion by 2032. The process of building ADUs traditionally involves complex land surveys and vendor consultations, but the introduction of a GenAI-powered ADU planning system seeks to simplify this. This innovative tool navigates city building codes and connects users with local vendors, offering viable floor plan options through a user-friendly app. The "ADU Planner" project, which won the top honor at the LlamaIndex RAG Hackathon, combines technologies like React, Flask, GPT-3.5/4V, and Google Maps to streamline the construction process. Users input their address to trigger a geocoding process that provides satellite imagery of their property, which is analyzed for building code compliance and potential obstructions. The system then suggests suitable ADU floor plans, allowing users to explore 3D renderings and pricing, facilitating initial discussions with builders. This approach aims to make ADU construction more accessible and tailored to individual needs while maintaining high standards of oversight and personalization.