Build vs Buy Decision Tool

The build vs buy decision is one of the most consequential software choices a business makes — and one of the most commonly under-analysed. Teams often default to buy because a shiny SaaS exists, or default to build because their engineers want to code. This tool scores 10 weighted criteria to give you a data-driven starting point for the conversation.

The four key criteria that matter most

Uniqueness of requirements: if your process is the same as thousands of other businesses (expense management, email marketing, CRM), buy. If your process is genuinely differentiated (proprietary pricing logic, unique workflow, custom data model), build. Competitive differentiation: software you compete on should be owned; commodity software should be bought. Integration depth: the more your needs require deep, bi-directional integration with your core systems, the more a custom build earns its cost. Existence of good off-the-shelf options: if three good products already cover 85% of your needs within budget, you need a compelling reason to build.

The hidden cost of buy decisions

SaaS costs are often underestimated. The advertised per-seat price is just the start — add integration cost, training time, workaround cost for the 20% the product does not cover, and the compounding effect of vendor price increases. A £300/month SaaS costs £3,600/year. Over three years with 15% annual price increases, that is over £12,000 — comparable to a custom build that perfectly fits your needs and that you own outright.