Every feature request triggers the same question: should we build this ourselves or buy an existing solution? The answer is rarely obvious, and getting it wrong costs 3-12 months of engineering time.
The Decision Matrix
Build When:
The feature IS your product's competitive advantage
- What makes your product different from competitors?
- If the answer is "our recommendation algorithm" or "our workflow engine" — build it
- Core IP should never depend on a vendor who might change pricing, shut down, or become a competitor
No existing solution fits your exact requirements
- You have evaluated 5+ options and none cover more than 60% of your needs
- The remaining 40% is not "nice to have" — it is critical to user satisfaction
- Workarounds to make an existing solution fit would be more complex than building from scratch
The feature needs deep integration with your domain model
- It needs to access internal data structures in ways no API could support
- Performance requirements demand in-process execution (not network calls to external services)
- The feature's logic is tightly coupled with your core business logic
You have the engineering capacity and expertise
- Your team has built similar systems before
- You can maintain it long-term (building is 20% of the effort; maintaining is 80%)
- The build timeline fits your product roadmap without blocking other priorities
Buy When:
The feature is commodity infrastructure
- Authentication, email sending, payment processing, file storage, search
- These are solved problems with battle-tested solutions
- Building your own auth system is almost never the right choice
Speed to market is critical
- You need the capability in days or weeks, not months
- The market window closes if you wait to build
- Buying now does not prevent building later once you understand requirements better
The feature is not your competitive advantage
- Analytics dashboards, CRM, notification systems, monitoring
- If it is not what makes customers choose you over competitors, buy it
Maintenance cost exceeds subscription cost
- A built solution requires ongoing engineering time: bug fixes, security patches, performance optimization, scaling
- If the engineering time to maintain equals 1-2 developer-months per year, a $500/month subscription is cheaper
Total Cost of Ownership: The Real Comparison
The mistake most teams make: comparing "cost to build" against "monthly subscription price." The correct comparison is 3-year TCO including all costs.
Build TCO (3-year)
| Cost Item | Estimate |
|---|---|
| Initial development | $20K-$100K (2-10 engineer-weeks) |
| Testing and QA | $5K-$20K |
| Documentation | $2K-$5K |
| Year 1 maintenance | 20-30% of build cost |
| Year 2 maintenance | 20-30% of build cost |
| Year 3 maintenance | 20-30% of build cost |
| Security patching (ongoing) | $5K-$15K/year |
| Scaling costs (if usage grows) | Variable |
| Opportunity cost (what else the team could build) | Highest cost, hardest to quantify |
Example: Custom analytics dashboard
- Build: 4 weeks × 2 engineers = $30K
- Annual maintenance: $8K
- 3-year TCO: $30K + $24K = $54K + opportunity cost
Buy TCO (3-year)
| Cost Item | Estimate |
|---|---|
| Monthly subscription | $100-$5,000/month |
| Integration development | $5K-$20K |
| Ongoing integration maintenance | $2K-$5K/year |
| Training and documentation | $2K-$5K |
| Data migration (if switching later) | $5K-$20K (risk cost) |
| Vendor risk (price increases, shutdown) | 10-20% annual increase assumed |
Example: Buy Mixpanel for analytics
- Monthly: $500/month = $6K/year
- Integration: $8K one-time
- 3-year TCO: $8K + $18K = $26K
In this example, buying saves $28K+ over 3 years AND frees engineering capacity for work that actually differentiates the product.
The Hybrid Approach: Buy Then Build
For features where the long-term answer is "build" but the short-term answer is "we need something now":
- Buy a solution today — get the capability immediately
- Learn from actual usage — understand real requirements, not hypothetical ones
- Build when constraints justify it — you now know exactly what to build based on real data
This approach has three advantages:
- Faster to market (weeks vs months)
- Requirements are validated before you invest in building
- You can build exactly what you need because you have used the bought solution and know its limitations
Decision Framework: Five Questions
For any build vs. buy decision, answer these five questions:
1. Is this our competitive advantage?
- Yes → Lean toward building
- No → Lean toward buying
2. How urgent is the need?
- Need it in 1-2 weeks → Buy
- Can wait 2-3 months → Either option is viable
- No urgency → Evaluate fully
3. Does a solution exist that covers 80%+ of our needs?
- Yes → Buy (the 20% gap is rarely worth building 100% for)
- No → Build (or combine multiple bought solutions)
4. Can we maintain it long-term?
- Yes (team has capacity and expertise) → Build is viable
- No (team is stretched, lacking expertise) → Buy
5. What is the switching cost if we choose wrong?
- Low (easy to migrate later) → Buy now, reassess in 12 months
- High (deep integration, data lock-in) → Invest more time in the decision
Common Build vs. Buy Mistakes
Mistake 1: "We can build it better" You probably can build a better authentication system for your specific use case. But Auth0 has 200 engineers working on security, compliance, and edge cases you have not thought of yet. Better is not always worth it.
Mistake 2: Not accounting for maintenance Building a feature takes N weeks. But maintaining it takes N × 3 over the next 3 years. Every built feature adds to your maintenance burden forever.
Mistake 3: Vendor lock-in fear Some lock-in fear is justified (database choices, core infrastructure). Most is not. If you build an abstraction layer over a bought solution, you can switch later. The risk of over-building to avoid lock-in often exceeds the lock-in cost itself.
Mistake 4: Not evaluating the market Before building, spend 2-4 hours surveying existing solutions. Many teams build features that excellent SaaS products already solve at $50-$200/month.
Mistake 5: Building to learn "We want to build our own search engine to learn how search works." Learning is a valid goal for personal projects. For your product, use Algolia or Elasticsearch and learn by building features your customers actually pay for.
When to Revisit the Decision
A buy decision should be revisited when:
- Vendor costs exceed $3K/month AND you have engineering capacity
- The vendor's limitations are blocking feature development
- You have outgrown the solution's scalability
- The vendor changes terms, pricing, or direction in ways that hurt you
A build decision should be revisited when:
- Maintenance is consuming more than 20% of a developer's time
- The feature is not differentiating (you built it for the wrong reasons)
- A new vendor emerges that solves the problem better than your custom solution
- The team that built it has left and no one wants to maintain it