TL;DRBuy SaaS when a product fits your workflow with minor compromise; build custom when the workflow is your edge, when per-seat pricing outgrows build cost, or when integration workarounds become their own unpaid software project. The framework below turns that instinct into arithmetic.
Start with fit, not philosophy
List the ten workflow steps that matter most in the process you are trying to fix. Score each candidate SaaS product honestly: native fit, configurable, or workaround. Two or more workarounds on steps you run daily is the warning line: each becomes standing manual labor, and their cost compounds monthly regardless of what the subscription costs.
Run the five-year multiplication
SaaS: seats times price times sixty months, plus expected tier increases, plus the wage cost of every workaround hour. Custom: build quote, plus roughly the build cost again spread across five years of support and change, plus hosting. Businesses are routinely surprised on both sides of this equation: subscriptions that quietly pass six figures, and builds whose maintenance was never budgeted. The multiplication takes an afternoon and reshapes the debate every time.
Weigh the risks that do not fit a spreadsheet
SaaS risk is dependency: price increases you cannot refuse, features deprecated mid-workflow, data export limits discovered at exit, and vendors acquired or sunset. Custom risk is stewardship: key-person exposure if one developer holds all knowledge, and rot if nobody owns updates. Both risks are manageable; only one of them is manageable by you. Documentation, explicit IP terms, and a support contract convert custom risk into a line item. SaaS dependency risk has no equivalent instrument.
Where the line actually falls
Commodity functions (email, accounting, payroll, CRM for standard sales motions) belong to SaaS almost without exception; the market has amortized their engineering across millions of users. The build case strengthens as the workflow becomes yours alone: pricing logic competitors do not share, operational sequences that define your service quality, data joins across systems no vendor connects. That is also where competitive advantage lives, which is why “too specific for SaaS” and “worth building” are so often the same sentence.
A decision you can defend
Write the fit scorecard, run the five-year math, and name the risks out loud. If SaaS wins, buy it without guilt and spend engineering only on integration. If the numbers say build, build with explicit IP terms, documentation, and support in the contract. Triton Foundry’s discovery process produces exactly this analysis, and roughly as often as not it ends with us recommending a product instead of a project.