How do I build a custom GPT for my business?

A custom GPT tailors AI responses to your business context — your products, processes, tone, and knowledge base. Three approaches, from simple to complex: Level 1 — GPT configuration (1-2 hours): Use OpenAI GPT Builder or Claude Projects. Upload your documents (product docs, FAQs, style guide), write custom instructions defining behavior and tone. Free with ChatGPT Plus. Limited but fast. Level 2 — RAG application (2-4 weeks): Build a retrieval-augmented generation system. Index your documents in a vector database, retrieve relevant context per query, send context + query to an LLM. More accurate than Level 1, supports API access, handles larger knowledge bases. Cost: $200-500/month for infrastructure. Level 3 — Fine-tuned model (4-8 weeks): Train a model on your specific data to permanently encode knowledge and style. Best for tasks where consistency and speed are critical. Requires 1,000+ high-quality training examples. Cost: $500-5,000 for training, then per-query inference costs. Start with Level 1 to validate the use case. Move to Level 2 when you need API access or accuracy improvements. Move to Level 3 only when RAG latency or cost is a bottleneck and you have sufficient training data.