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Build Versus Buy Decision Tree

By Graham O'Shea, Founder and Lead Developer  ·  1 August 2026  ·  Part of The Agentic AI Guide

The build or buy decision has a published test, and it is a question about your business rather than about software. This tree walks it in order.

What Is In The Build Versus Buy Decision Tree

  • How to state the function without naming a product.
  • The differentiator test, with three questions that answer it.
  • The risk asymmetry, and how to check your answer against it.
  • The integration line, and why it belongs in both columns.
  • An honest total, including the cost of adapting your process.
  • What heavy customisation of a bought package usually means.
  • How to re-run the test on systems you already own.

Why It Starts With The Function

Fowler's test turns on whether the underlying business function is a differentiator. That is a question about your business, not about software, which is why it survives changes in the software. Starting from a product shortlist skips it, and the shortlist then decides the answer.

The full reasoning is in the article this accompanies: How To Decide Whether To Build Or Buy.

Prefer A Second Opinion On The Build Or Buy Call?

The scoping audit is free. The form asks for your website or store URL and a note on what is eating the time, and a decision you are weighing up is a reasonable thing to put in that box.

Request The Free Scoping Audit