The four options, in order.
Buy. Somebody has already built this and it fits your process without damaging workarounds. This is the right answer far more often than people who enjoy building want it to be.
Configure. It nearly fits, and the gap closes with settings, fields and workflow configuration inside the product. Cheaper than it looks, and frequently already paid for.
Integrate. Each system is fine at its own job and the problem is the space between them. This is the most commonly misdiagnosed case — it presents as "our software is bad" when the software is fine and disconnected.
Build. None of the above is honestly true. Now you are building, and you should know exactly why the first three failed.
The question that actually settles it.
Not "can we build this" — you almost certainly can. The question is: who owns it in five years? Custom software needs hosting, dependency updates, security patching, and someone who understands why it works the way it does. That is a permanent operating commitment, not a project cost.
If you cannot name the person or the arrangement that covers that, buy something. A product that fits at 80% and is somebody else’s responsibility to maintain will beat a perfect system that nobody owns.
Two signals that building is genuinely right.
The process is a competitive difference. If how you do this thing is part of why customers choose you, software that forces you to do it the standard way is removing your advantage to save a license fee.
Per-seat economics have inverted. On a large team, per-seat licensing for a system used by everyone can pass the cost of building. That is a real calculation rather than a feeling, and it should be done with the maintenance cost included on the build side.
If you do build, build in stages.
The failure mode of custom software is a year-long build revealed at the end, at which point the requirements have moved and the people who specified it have changed their minds legitimately. One real workflow, in production, used by real people, teaches more than any amount of specification — and it gives you the option to stop.