Build-vs-buy decisions are fundamentally about where you want to invest your finite engineering attention. Every tool you build is attention diverted from your core product; every tool you buy is a dependency you don't control.
We use a simple framework: build when the capability is core to your differentiation, buy when it's table stakes. But the nuance is in defining what 'core' means for your specific business.
Consider also the trajectory of your needs. A tool that fits today might constrain you tomorrow. Sometimes building a simple version now preserves optionality better than buying a comprehensive solution.
Finally, don't underestimate the cost of integration. Buying is rarely plug-and-play. The total cost includes configuration, training, workflow changes, and ongoing vendor management.