Build vs Buy
The decision framework every CTO faces — when to build, when to buy, and when to compose.
The build-buy spectrum
Two different lenses depending on what kind of capability you're evaluating.
When building wins
Capabilities that justify the investment in custom engineering
- Justified
- High
- Necessary
- Last resort
Building is expensive — but for your core differentiator, it's the only option that compounds.
When buying wins
Capabilities where speed and maturity outweigh control
- Low
- Medium
- Medium
- Trade-off
Buying is fast — and for commodity functions, your engineers have better things to build.
The key concepts
Click each concept to see the business analogy and visual explanation.
The real price tag
Total Cost of Ownership
"Buying a house vs renting — the mortgage is just the start"
The licence fee is the estate agent's brochure. The real cost is the mortgage, insurance, maintenance, renovations, and the time you spend fixing the boiler on a Sunday. Build projects have the same hidden layers: hiring, onboarding, infrastructure, on-call rotas, and the opportunity cost of everything else your team isn't building.
At WPP, every build-vs-buy decision went through a 3-year TCO model. The surprise was never the headline cost — it was the integration, training, and ongoing maintenance that doubled or tripled the sticker price.
The real price tag
Total Cost of Ownership
"Buying a house vs renting — the mortgage is just the start"
The licence fee is the estate agent's brochure. The real cost is the mortgage, insurance, maintenance, renovations, and the time you spend fixing the boiler on a Sunday. Build projects have the same hidden layers: hiring, onboarding, infrastructure, on-call rotas, and the opportunity cost of everything else your team isn't building.
At WPP, every build-vs-buy decision went through a 3-year TCO model. The surprise was never the headline cost — it was the integration, training, and ongoing maintenance that doubled or tripled the sticker price.
Switching costs
Vendor Lock-in
"Changing banks — possible but painful enough that you never do"
Every year you stay, the switching cost climbs. Your data is in their format, your team knows their API, your workflows assume their quirks. It's not that you can't leave — it's that leaving gets more expensive every quarter. The vendor knows this, and prices accordingly.
Lock-in isn't binary. Map your exit cost at 1 year, 3 years, and 5 years. If the 5-year exit cost exceeds the cost of building, you've just rented yourself into a more expensive mortgage.
Strategic filter
Core vs Context
"A restaurant cooks its own food but doesn't grow its own wheat"
Core is what makes you different — the thing customers pay for. Context is everything else: payroll, email, logging, CI/CD. The strategic question isn't 'can we build this?' — it's 'should we spend our best engineers on this, or on the thing that actually differentiates us?'
Most teams over-classify things as 'core'. If three competitors use the same vendor for it and customers don't notice, it's context. Build only what creates competitive distance.
Hidden cost
Integration Tax
"Every new appliance needs a different adapter"
Each vendor has its own auth model, data format, error convention, and upgrade cycle. Your engineers become glue-code specialists — translating between systems instead of building value. By the third integration, you're not buying productivity; you're buying complexity.
The integration tax compounds. System A talks to B, B talks to C. Now A changes its API. The blast radius isn't one system — it's every downstream dependency. Budget 30-40% of vendor cost for integration and maintenance.
The CTO's real answer
The Hybrid Path
"You don't build or buy — you compose"
The real answer is almost never pure-build or pure-buy. You build the core differentiator, buy the commodity layers, and wrap everything in an abstraction that lets you swap vendors without rewriting your product. The architecture is the strategy.
At WPP, the cloud platform was a hybrid: custom orchestration layer (built) on top of hyperscaler primitives (bought). The abstraction layer was the strategic asset — it let us move workloads between providers without rewriting applications.
Decision framework
Is this capability your competitive advantage?
Yes → build (or acquire). No → buy.
Can you staff and retain a team for this?
No → buy, even if building looks cheaper on paper.
Will the vendor's roadmap diverge from yours?
Yes → build an abstraction layer now. Review annually.
Is the integration cost greater than the build cost?
Often yes for the 3rd+ vendor. Factor integration into every buy decision.