Option Generation
Ask for plausible architectures and bought solutions with trade-offs
- Reduces tunnel vision
- Surfaces non-obvious alternatives
- Accelerates early discovery
software-development16 min read
Build vs Buy: Decision Framework for Custom Software
A practical decision framework to choose between building custom software and buying an off-the-shelf product—grounded in differentiation, time-to-value, TCO (including run and change costs), integration complexity, compliance, and exit feasibility.
By Solution Engineering Team
Summary
Use this framework to decide whether to build custom software or buy a product. Score options on differentiation, time-to-value, total cost of ownership (build + run + change), integration/UX coherence, security & compliance, data portability, and exit feasibility.
Decision Criteria
| Criterion | Signals (What to Look For) | Evidence |
|---|---|---|
| Differentiation | Core to strategy, brand, unique workflows, or regulated edge cases | Strategy doc linkage, customer interviews, win/loss notes |
| Time-to-Value (TTV) | Pilot feasibility, dependency risk, availability of SMEs | Proof-of-value plan, critical path, calendar time |
| TCO (12-24 mo) | Build + run + change + support + training + exit | Cost model (infra, licenses, tokens/GPU if AI, ops, migration) |
| Integration & UX Coherence | APIs/webhooks/SDKs fit, SSO/SCIM, shared nav, consistent UX | API coverage matrix, demo screenshots, latency budgets |
| Security & Compliance | AuthZ model, data residency, auditability, SBOM/SLSA, DLP | Threat model notes, control mapping, pen/vuln findings |
| Vendor/Community Viability | Financials, roadmap, release cadence, SLA, support quality | Release history, CVE cadence, support tickets/trials |
| Extensibility & Lock-In | Plugin/extension model, data export, no black-box data | Adapter prototype, export/import test, schema mapping |
| Operate & Evolve | SLOs, observability, upgrade path, staffing reality | Runbooks, on-call plan, upgrade rehearsal notes |
Quick Trade-Offs at a Glance
Using AI to Evaluate Options
Evidence Synthesis
Summarize docs, API refs, logs, and benchmarks into briefs
- Shared understanding
- Faster brief prep
- Traceable citations
Prototype Scaffolds
Generate adapters/tests for quick PoV spikes
- Faster validation
- Higher signal from PoV
- Reusable spikes
Guardrails
Redact secrets/PII, restrict data, log prompts, require human sign-off
- Privacy & IP protection
- Auditability
- Trustworthy usage
Proof-of-Value (2-3 Weeks)
Time-boxed evaluation workflow
Frame
Define outcomes, constraints, SLOs, and evaluation criteria
- Evaluation brief
- Success metrics
Spike
Build adapter/prototype; integrate auth/SSO; validate key APIs
- Spike repo/branch
- Demo & notes
Security & Data
Threat thinking, data mapping, dependency scan, basic DLP
- Risk notes
- Control mapping
TCO & Ops
Model build/run/change/exit; define runbooks and SLO budgets
- TCO model (12-24 mo)
- Ops plan
Decide
Compare options against criteria; record rationale and owners
- Decision record
- Rollout/rollback plan
Anti-Patterns to Avoid
Tool-First Decision
Choosing technology before defining problem statement and SLOs
- Leads to misaligned solutions
- Increased technical debt
- Poor business fit
Integration Assumptions
Assuming Buy is faster without validating data flows and APIs
- Hidden complexity costs
- Extended timelines
- Poor user experience
Cost Blindness
Assuming Build is cheaper without modeling change/ops and staffing
- Budget overruns
- Hidden operational costs
- Staffing gaps
Vendor Lock-In
No exit path—black-box data or proprietary schemas with no export
- Reduced flexibility
- Migration challenges
- Vendor dependency
Security Deferral
Skipping security/privacy until late; rework explodes TCO
- Compliance violations
- Security vulnerabilities
- Costly rework
Analysis Paralysis
Infinite discovery; no time-boxed PoV or decision deadline
- Missed opportunities
- Team frustration
- Delayed value delivery
Decision Checklist
- Outcomes and SLOs defined; criteria agreed
- Two viable options with trade-offs and exit feasibility
- TCO modeled (build + run + change + support + exit)
- Security/compliance and data flows assessed
- Integration/UX demoed with latency targets
- Decision record captured; rollout/rollback defined
- 30/90-day checkpoints scheduled
Prerequisites
- Clear business outcomes, SLOs, and constraints
- Access to API docs, trial licenses, or sample datasets
- Agreement on data/privacy guardrails and security review
- Capacity to run a 2-3 week proof-of-value and capture a decision record
References & Sources
- Architecture Decision Records (ADR)— Comprehensive guide to documenting architecture decisions and patterns
- NIST Secure Software Development Framework— Security guidelines for software development and procurement decisions
- OWASP Application Security Verification Standard— Security verification standards for application development and procurement
- SLSA Supply Chain Levels— Framework for securing software supply chains in build vs buy decisions
- DORA Research— Research on software delivery performance and technical decision quality
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