Short answer: buy when the workflow is conventional and supported; build when the behaviour is central to your identity, must integrate deeply, or the compromises cost more than ownership.
Prefer existing software when
The requirement is common, configuration covers it, and the maintainer publishes a credible support and migration path.
Consider custom work when
Your mechanic differentiates the server, connects several systems, or needs operator workflows that generic products cannot express safely.
Account for ownership
Custom code creates control and responsibility. Plan testing, documentation, version updates and knowledge transfer—not only initial delivery.
Explore the related MCMinelab solution