Start with the business advantage
A custom build makes sense when the workflow is central to how your company competes. If the requirement is common and does not differentiate the business, established software may be a faster and less risky choice. Start by identifying what truly makes the operation unique.
Count the whole cost
Compare licensing, implementation, integration, training, maintenance, hosting, and the future cost of changing course. A low initial subscription does not always mean the lowest total cost; a custom build also brings ongoing responsibilities.
Test your assumptions early
Before committing to an ambitious roadmap, prototype the critical workflows, identify integration constraints, and measure the cost of the manual alternatives. Better evidence produces better architecture decisions.