How to Build a Custom GPT That Writes Estimates

A custom GPT that writes estimates is just an AI assistant with standing instructions about your trade, your estimate format, and your rules (never invent prices), plus a sample estimate or price list. One catch: as of October 2026, OpenAI says personal ChatGPT accounts can no longer create new custom GPTs and it plans to retire them. You can build the same estimate writer today with the instructions below, saved in whatever reusable-instructions feature your AI app offers, or pasted at the start of a chat.

Steps

1. Pick where it will live. If you're on a business ChatGPT workspace that still allows GPT creation, you can use Explore GPTs, then Create. Otherwise, use your AI app's saved project or custom-instructions feature (ChatGPT, Claude, and Gemini each have one; names and plan limits change, so check your app). The no-setup option: keep the instructions in your phone's notes and paste them at the start of a new chat.
2. Name it something like "[COMPANY] Estimate Writer."
3. Paste the instructions below as its standing instructions.
4. Upload one or two of your real past estimates (remove customer names and addresses) and, if you have one, your price sheet.
5. Test it with notes from a real job. Fix the instructions until the output matches how you'd write it.
6. Keep it private. Don't share an assistant that contains your pricing.

You write estimate drafts for [COMPANY], a [TRADE] business in [AREA].
When I paste job notes, return:
1. A one-line job title.
2. Scope of work as short bullet points in plain language.
3. Line items: description, quantity, unit, unit price, total. Use prices ONLY from the attached price sheet. If an item isn't on the sheet, write [PRICE NEEDED] instead of guessing.
4. What's not included (exclusions), based on my notes.
5. A 3-sentence summary a homeowner can understand without trade terms.
Rules: never invent prices, permits, warranties, or code requirements. If something in my notes is unclear, list your questions at the end instead of assuming. Keep my tone: plain, friendly, professional.

AI writes the first draft. Read it before you send and fix any price, date, or promise you didn't check yourself.

Source on custom GPT changes: OpenAI Help Center, Creating and editing GPTs (checked Oct 2026).

Don't upload customer personal information. Strip names, phone numbers, and addresses from sample estimates first.