Buy when a mature tool supports the workflow without distorting it. Build when the workflow is strategically important, unusually specific, or depends on data and integrations that packaged software cannot support cleanly. The right answer may also be a hybrid: buy the commodity layer and build the differentiating workflow around it.
Start with workflow fit
List the user, decisions, records, exceptions, and systems involved. A SaaS tool is a strong choice when it supports those needs with modest configuration. Custom software becomes more defensible when workarounds create repeated manual handoffs, poor visibility, or compromised decisions.
Compare lifetime ownership, not only build cost
Include subscriptions, implementation, migration, integration, customization, internal administration, vendor limits, maintenance, security, support, and future change. A lower first-year price can still create a higher long-term operating burden.
Separate commodity from differentiation
Authentication, email, payments, storage, and observability are often better purchased or integrated. The workflow, data model, and decision surface that make the business distinct may be worth owning.
Choose a reversible first step
Test the decision with a narrow integration, internal tool, or critical-path release. Define what evidence would justify expanding the custom system and what conditions would send the team back to an off-the-shelf option.
Build-or-buy decision matrix
| Decision factor | Prefer SaaS | Prefer custom |
|---|---|---|
| Workflow fit | Standard workflow fits | Workflow is differentiating |
| Time to value | Need a mature tool now | Can ship a narrow owned path |
| Integration | Supported connectors are enough | Data and systems need custom logic |
| Ownership | Vendor limits are acceptable | Control and extensibility matter |
Use this as a starting filter, then confirm the choice against the actual workflow and constraints.
Decision checklist
- List users, decisions, records, exceptions, and systems for the workflow.
- Compare lifetime ownership: subscriptions, integration, administration, change.
- Separate commodity layers from the differentiating workflow.
- Choose a reversible first step and the evidence that would expand it.
Common mistakes
- Comparing first-year price instead of lifetime ownership.
- Building commodity layers like authentication or email from scratch.
- Forcing a differentiating workflow into a tool that distorts it.
- Committing to a full custom system with no reversible first step.
