To build a generative AI (GenAI) application, first, choose a suitable model like GPT or a diffusion model. Next, gather and preprocess relevant data for training. Fine-tune the model using domain-specific data to enhance performance. Develop a user-friendly interface for interaction, ensuring it integrates well with the AI model. Finally, rigorously test the application to ensure accuracy and reliability before deployment. Continuous updates and monitoring are essential for maintaining performance.