To build an InvestorGPT AI chatbot on WhatsApp using Django, Twilio, and the ChatGPT API, developers need to set up their environment, configure their database, create a Twilio-approved webhook, and integrate OpenAI's API. The chatbot logic will be handled by a view function that extracts data from incoming requests, calls the OpenAI API to generate a response, stores the conversation in the database, and sends the response back to the user via WhatsApp. With this setup, users can send messages to the chatbot, which will respond with generated text using the GPT-3.5 turbo model. The chatbot is tested by sending sample questions or prompts and receiving responses from the AI model.