When to Build Custom vs Buy SaaS

Buy versus build is as old as software itself, but the answer has shifted. The traditional calculus was simple: buying was almost always cheaper and faster. Building was almost always a mistake unless you had a very specific need and a team to maintain it. That calculus assumed custom software was expensive. It's getting a lot less expensive.

Start with SaaS when the problem is well-understood and you're not competing on the workflow it supports. Accounting, email, CRM for a standard sales process, project management — solved problems. The vendors have spent millions on edge cases you haven't thought of yet. You'll waste money trying to replicate what they've built, and end up with something worse.

Build custom when the SaaS is fighting you. You know the feeling. You're spending more time working around the tool's limitations than doing actual work. Three different products duct-taped together with Zapier because no single one does what you need. Your team has developed elaborate workarounds that new hires learn like institutional folklore.

When the tool shapes your process instead of the other way around, that's a sign.

Build custom when the workflow is your competitive advantage. If the way you handle customer onboarding is why clients choose you over competitors, you probably shouldn't run it on the same platform everyone else uses. Custom software that encodes your unique process becomes a moat. SaaS that everyone has access to doesn't.

There's a middle ground: build custom where it matters, integrate with SaaS everywhere else. Use Stripe for payments, SendGrid for email, Postgres for your database — then build the business logic layer that ties them together. You get the reliability of proven infrastructure with custom logic where you need it. With AI-assisted development, this kind of targeted build is realistic for small teams, not just enterprises.