Over coffee with a founder recently I heard a familiar lament: "We spent nearly a year building our own data-pipeline engine, and now the VC is grilling us on why we didn't use a proven vendor". A week earlier, an investor complained that one of their portfolio companies was so tightly tied to a proprietary product that any pivot would trigger legal wrangling and year-long rewrites. Go figure...

Whether you build technology yourself or buy it off the shelf can raise enterprise value, or introduce future friction during diligence. Investors dig hard into these decisions because every choice implies something about cost, speed, and eventual exit readiness.

Why build-versus-buy sits on the due diligence critical path

First comes strategic importance. If a component is part of the competitive moat, home-grown innovation makes sense. McKinsey found that companies investing in genuinely differentiating tech outpace peers by ~20% in revenue growth. But when the capability is commodity (think payments, CRM, off-the-shelf observability) buyers prefer to see a battle-tested vendor so the team can stay laser-focused on its real secret sauce.

Second is the uniqueness of requirements. Off-the-shelf tools cover the 90% case. When your workflows are truly novel (e.g.: a proprietary machine-learning pipeline) custom code avoids painful compromises. Netflix famously built its recommendation engine in-house because no vendor could match the scale and accuracy they needed.

Then there is time-to-market and total cost of ownership (TCO). Buying nearly always ships faster, arrives with support, and converts capex to predictable opex. Building absorbs more engineers up front, but once a solution is heavily used the per-transaction cost may drop well below perpetual license fees. Diligence teams want to know how you did the maths.

Finally, investors examine risk tolerance and vendor lock-in. Commercial software shifts some operational risk to the vendor but introduces dependency: contract renewals, price increases, data-migration headaches. Custom code hands you control yet exposes you to delivery and maintenance risk. Showing how you balanced those forces tells buyers you well understand the considerations and keep future choices open under your control.

Taken together, build-versus-buy choices reveal how a team balances innovation, speed, cost and optionality. They influence gross margin, scalability and even integration complexity during a carve-out or acquisition.

How investors weigh the decision

Investors use a simple framework:

  1. Core vs. commodity: they ask: "Is this function part of the company's competitive moat or table stakes?" Founders should be able to articulate which components differentiate the product. If everything is built in-house, they will probe whether resources are misallocated.
  2. Economic analysis: investors model the TCO for both options: license fees, cloud spend, engineering salaries, maintenance and upgrade cycles. They also factor in time-to-value: a delayed launch can erode first-mover advantage.
  3. Exit readiness: a stack littered with proprietary licenses can slow down an IPO or trade sale because renegotiating vendor contracts takes time. Conversely, deep bespoke code with no documentation scares buyers because key engineers may walk away. Due diligence will ask about vendor termination clauses, escrow arrangements, and the portability of custom code.
  4. Governance and roadmap control: a vendor's roadmap may diverge from your needs, while in-house teams risk falling behind on maintenance. Investors might look for evidence that you review vendor roadmaps quarterly, negotiate SLAs that match your SLOs, and allocate capacity for refactoring home-grown components.

Signals that raise eyebrows

Investors notice when teams write bespoke billing engines or identity providers while world-class SaaS alternatives exist and they read it as opportunity cost. They worry when a critical module is tied to a single vendor, yet no migration path exists. They flinch at opaque TCO spreadsheets or, worse, decisions made by gut feel. And they downgrade valuation if the codebase is full of clever features but no clean APIs exist. This shows lack of integration maturity. Investing heavily in custom features without mature APIs or integration hooks hampers partnership opportunities and future acquisitions.

Habits startups should adopt

  • Document your rationale: keep a build-vs-buy decision log. For each component list the strategic importance, alternatives considered, estimated build cost and TCO, vendor pricing, and exit plan. Investors love seeing that you compare options systematically.
  • Prototype before buying: for third-party solutions, run a proof of concept. Evaluate integration complexity, performance, and vendor responsiveness before signing.
  • Have a vendor assessment process in place: Check the service not only from the technical aspect, but also from the legal, security and data privacy angles.
  • Review decisions periodically: a choice that made sense at Seed might not fit at Series B. Schedule annual reviews of home-grown modules and vendor contracts. Cloud-native SaaS options improve quickly so your bespoke feature may no longer justify its maintenance burden.
  • Negotiate portability: when you do license software, negotiate termination assistance and data-export clauses up front (the EU Data Act will be on your side). Ideally ensure that you can extract your data and run the service in a private cloud if the vendor is acquired or fails to meet SLOs.
  • Calculate payback: use a simple ROI calculator: compare development cost and delay against subscription fees and license renewals. Assign probability and margin of error to your estimates.

Mini-Glossary

  • Vendor lock-in: Switching away from a third-party product incurs high costs (proprietary formats, long contracts).
  • Total Cost of Ownership (TCO): Full life-cycle cost - build or purchase, hosting, upgrades, training, support.
  • Strategic differentiator: A capability that truly separates you from competitors, worth bespoke investment.
  • Commodity function: A standard need (e.g., payroll, CRM) where buying saves time and cash.

Your turn

When did a build-vs-buy decision bite you, or save the roadmap? Did custom code become a moat, or did vendor lock-in stall a pivot? Share the story below, scars teach best.

Founders: Need help auditing your build-vs-buy ledger before the next round? Let's talk.

Investors: Looking to benchmark vendor-lock exposure across your portfolio? I can help.

Next in the Playbook

Edition 8 will look at "Security & Compliance in the AI-Act Era": how emerging EU rules and baseline security metrics are reshaping diligence checklists for both SaaS vendors and their investors. Subscribe and it will land in your inbox.

Originally published on the Tech Due Diligence Playbook newsletter on LinkedIn.