A custom app is not automatically better than an existing one. It gives you control, but it also gives you code to maintain, permissions to manage, edge cases to support and a release process to own. Start by asking whether the problem is important enough to justify that responsibility.
Check the existing options first. Can an app handle the workflow without forcing your team to change how it operates? Does it support your Shopify plan, markets, checkout setup and other installed apps? Can the vendor explain how data is stored, how support works and what happens if you leave?
A custom build becomes more reasonable when the workflow is central to the business, the available apps create expensive workarounds, or the rules are specific to your operation. It can also make sense when you need a private tool for multiple stores, a controlled merchant experience or an integration that does not exist yet.
Before building, write down the smallest useful version. Define the users, the inputs, the decisions, the outputs and the failure cases. Decide which parts need to be configurable and which can remain fixed. This turns a vague request into a build that can be tested and stopped at a sensible milestone.
The right answer is sometimes an existing app with a small integration around it. The right answer is sometimes a private app. The goal is not to own more software; it is to remove the constraint without creating a bigger one.