Build from scratch vs. customise an existing ERP: a practical decision framework
Most vendors will push you toward the answer that benefits their business model. Here is how to make the decision based on your actual situation.
The default assumption is wrong
Most businesses default to customising an existing ERP (SAP, Odoo, Microsoft Dynamics) because it feels safer — the platform is proven, the community is large, and the timeline seems shorter. This assumption is correct in a small number of situations and misleading in the majority of them. Customising a heavyweight ERP to match a non-standard business process is frequently more expensive, slower, and more technically constraining than building the right system from scratch.
When to customise an existing platform
Customisation makes sense when your business processes are genuinely standard — when the way your industry operates matches the assumptions built into the ERP. It also makes sense when you have a large, geographically distributed organisation with established IT governance — where the community support, compliance certifications, and vendor liability of a major ERP platform matter more than flexibility. If you are a medium-sized business with a fairly conventional operating model, customising Odoo or a similar open-source ERP can be the right call.
When to build from scratch
Build from scratch when your business model is genuinely non-standard — when the workflow you need does not exist in any off-the-shelf system and customising one would mean fighting the platform at every step. Also build from scratch when you need deep integration with proprietary systems, government APIs, or industry-specific data formats that no general ERP handles well. And build from scratch when you want to own the code — when you cannot accept per-seat licensing that scales with your headcount indefinitely.
The hidden cost of customisation
Every customisation of an existing ERP creates technical debt relative to the base platform. When the vendor releases a major update — which they will — your customisations either break or require expensive re-work. This upgrade tax compounds over time and is rarely factored into the original business case. We have seen organisations trapped on unsupported versions of major ERP platforms because the cost of upgrading with their customisations is prohibitive.
The practical decision framework
Ask yourself three questions: First, is more than 30% of your required functionality genuinely non-standard? Second, do you need integration with systems that the ERP platforms do not support natively? Third, do you want to eliminate recurring per-seat licensing in the medium term? If the answer to two or more of these is yes, a custom build is likely the correct economic decision — even if the upfront cost is higher. If the answer is no to all three, customise.
The honest answer for most SMEs
For most small and medium enterprises, the right answer is a hybrid: a lean custom-built system for your most differentiated processes, integrated with best-of-breed SaaS tools for commodity functions like accounting, payroll, or HR. You do not need to build everything — you need to build the things that are genuinely unique to your business.
This is a decision we help clients make at the start of every ERP engagement — before any code is written. If you are facing this question, a structured discovery conversation is worth more than any vendor demo.