Building custom software is attractive, but an existing SaaS tool is often cheaper and faster when it supports the core process well. Here is a decision framework from an agency that also builds custom software.
Always start with buying
The default should be: buy SaaS. Build only when no tool fits. Why?
- Time-to-value: SaaS runs tomorrow. Custom 6 weeks later.
- Maintenance is someone else's: updates, security, hosting, not your problem.
- Proven approach: SaaS makers learned from 1000 customers, you get that intelligence free.
- Predictable costs: €X/month. No scope creep, no maintenance surprises.
Rule: If your SaaS tool already does 80% of what you need, use it. Don't build for the last 20%.
When to build
Custom software is the right call when:
- It's your core differentiator: software that makes your business different from competitors.
- SaaS tools don't fit: workflow so specific no tool covers 50%+.
- Volume makes SaaS expensive: €5/user/mo × 200 users = €12k/year. That's custom budget.
- Data sovereignty is critical: compliance or confidentiality demands an own stack.
- You integrate 5+ systems with no standard connections.
Concrete examples
From recent projects:
- Hotel late check-in: built custom. No SaaS does this for independent hotels. ROI in 8 months.
- Bookkeeping: we recommended Moneybird instead of custom. €30/mo, 2-week setup, done.
- Client CRM: custom. Client had 4 SaaS tools side by side. One custom dashboard replaced them all.
- Newsletter: we recommended Mailchimp. Building costs more than €600/year in licenses.
Numbers: Custom software break-even vs SaaS typically lies between €8,000 tot €25,000 investment, with TCO advantage after 18-36 months, depending on volume and complexity.
Conclusion
Building isn't better than buying, it's different. Make the choice based on strategic impact, not feel. A good conversation with your agency shouldn't lead to a quote, it should lead to honest advice.