Teams often default to building because it feels controllable, or buying because it feels faster. Both defaults can be wrong.
Build when the workflow is differentiated and creates durable advantage. Buy when the process is commodity and the market provides a mature product. Integrate when the gap is connection, not capability.
Also price the hidden costs: internal maintenance, vendor lock-in, security responsibility, and change management.
The best advisory engagements make this decision explicit before delivery begins.