Module 1.5: Build vs Buy Economics
The most expensive engineering decision you make repeatedly. Master Total Cost of Ownership, integration debt, vendor lock-in analysis, and the differentiation test.
🎯 What You'll Learn
- ✓ How to calculate 5-year TCO for build decisions (development + maintenance + opportunity cost)
- ✓ How to evaluate true buy costs (license + integration + lock-in + customization)
- ✓ The Differentiation Test for build-vs-buy decisions
- ✓ How to create a Build vs Buy decision matrix
Lesson 1: The True Cost of Building
Engineers consistently underestimate the cost of building because they measure development time, not Total Cost of Ownership (TCO). Building includes ongoing maintenance, infrastructure, on-call, documentation, and hiring to support the system.
The visible part: engineer-hours × burdened cost rate. A 3-month project with 2 engineers at $150K/yr burdened = ~$75K in development cost.
Bug fixes, security patches, dependency updates, performance tuning. Rule of thumb: annual maintenance = 15-20% of initial development cost. Over 5 years: equals or exceeds the build cost.
The features you DIDN'T build because your team was building infrastructure. If those features would have generated $500K in revenue, that's the real cost.
Custom systems create knowledge silos. When the original developer leaves, replacement cost is 3-6 months of reduced velocity while the new person ramps up.
Pick one internal tool your team built. Calculate 5-year TCO: initial development + annual maintenance × 5 + opportunity cost of the time.
Lesson 2: The True Cost of Buying
Buying seems simple ("just pay the vendor"), but hidden costs include integration, customization, data migration, training, and the ongoing risk of vendor dependency.
The sticker price. Enterprise SaaS: $50K-$500K/year. But this is usually less than half of the true cost of buying.
Every external tool needs integration: API connections, data transformations, error handling, monitoring. Each integration is a maintenance surface area you now own.
Once your data and workflows are in a vendor's system, switching costs are enormous. The vendor knows this — expect above-inflation price increases at renewal.
You start with "out of the box." Within 12 months, you've built custom integrations, workflows, and workarounds. These customizations become unmaintainable as the vendor releases new versions.
For a tool you currently buy, calculate true TCO: license + integration cost + team time managing it + switching cost if you left.
Lesson 3: The Decision Framework
The build-vs-buy decision should be made on a simple principle: build what differentiates you, buy what commoditizes you. Your competitive advantage should never depend on a vendor.
Does this capability differentiate you from competitors? If yes: build. If no: buy. Example: a unique recommendation engine = build. A CRM = buy.
Buying gives you 80% of functionality in weeks. Building gives you 100% of functionality in months. Is the extra 20% worth the months of delay?
Do you have the team to build AND maintain this system long-term? Building authentication is easy. Maintaining it through OWASP trends, compliance changes, and scaling is a different story.
Create a Build vs Buy decision matrix for 5 components in your stack. Score each on: differentiation (1-5), time-to-value (1-5), maintenance burden (1-5), and team capability (1-5).