Build vs buy software: when custom development pays off

Most organisations eventually reach the point where a spreadsheet, a pile of SaaS subscriptions or an ageing internal system no longer fits how the business works. The choice is then to buy an off-the-shelf product and adapt your process to it, or to build software around your process.

This post is for operations leaders, CTOs and founders making that call for internal tools or customer-facing platforms. We build custom software for a living, so we will say it plainly: buying is often the right answer. The aim is to know which situation you are in before you commit budget.

• Buy when the process is common across companies and gives you no advantage.
• Build when the process is how you win, when integrations are the product, or when available tools force workarounds that cost more than software would.
• Combine when a bought core covers most needs and a thin custom layer handles what makes you different.

Off-the-shelf products have many customers paying for their development, security work and support. For standard problems, that is hard to match. Buying usually wins when:

• The process is standardised by law or convention, such as payroll, accounting, HR records, email or e-signatures.
• Your requirements match what the product already does, with configuration.
• You need it working within weeks and have no engineering team to own software.
• The vendor's roadmap is heading where you are heading.
• The compliance certifications you need, such as SOC 2 or ISO 27001, are already in place.

If a product covers the requirements that matter and the gaps are nice-to-haves, buy it and adapt the process. Custom software built to close small gaps rarely pays back.

Building makes sense when the software carries value that no vendor sells. Typical signals:

1. 01The workflow is your advantage. How you price, match, plan or assess risk is why customers choose you, and a generic tool would flatten it.
2. 02You are paying for workarounds. Staff re-key data between systems, maintain shadow spreadsheets or run manual checks because the tool does not fit.
3. 03Integration is the hard part. The value comes from connecting your ERP, CRM, data warehouse and partner APIs in ways no single product does.
4. 04Per-seat pricing grows faster than the business. At scale, licences for hundreds of users can exceed the cost of owning the software.
5. 05You want to sell it. A customer-facing platform or SaaS product is custom development by definition.
6. 06AI is part of the workflow. Agents, document parsing or retrieval over your own data usually need to live close to your systems and your data rules.

Comparing a subscription price with a build quote is misleading, because both options have costs that only show up later. Compare them over three to five years:

Price the workarounds explicitly. If, for example, six people each spend an hour a day moving data between two systems, that is a known annual cost you can put next to a build estimate. It is often the largest line that nobody has written down.

On the build side, plan for maintenance from day one. Budget each year for dependency updates, security patches, small changes and hosting. Software that is built and then left alone decays.

Feature comparison tables get most of the attention in a buying process. In our experience, integrations decide whether a system works in daily use. Before choosing either route, map out:

• Which system holds the source of truth for each type of data: customers, orders, products and documents.
• Which way data must flow, how often, and who resolves conflicts.
• Which APIs exist, their rate limits and whether they expose the fields you need.
• What happens when an integration fails: retries, alerts and reconciliation.

If a bought product has a good API and webhooks, a thin custom layer can often close the gaps without building the whole system. This hybrid approach is common and frequently the best value.

The classic risks of custom software are overruns, a system nobody can maintain and dependence on a single supplier. You can manage all three:

• Start with the smallest version that replaces a real workflow for real users, and release it within weeks.
• Choose mainstream technology your future team can hire for.
• Make sure code, infrastructure and data sit in accounts you own from day one.
• Insist on automated tests, documentation and a clear handover path.
• Fix the scope per phase, so budget is committed in steps you can review.

Agentic engineering, where senior engineers work with coding agents, has also lowered the cost of building well-defined software. That moves some decisions that were clearly on the buy side a few years ago. Our post on agentic engineering for SaaS explains how.

1. 01Describe the workflow and mark which parts are standard and which set you apart.
2. 02Shortlist two or three products and test them against your five hardest real scenarios, including integrations.
3. 03Price the workarounds each product would leave in place.
4. 04Estimate the five-year cost of buying, building and a hybrid of the two.
5. 05Take the lowest total cost for the parts that do not differentiate you, and invest in the parts that do.

We tell clients when a product they can buy is the better choice. When custom software is the answer, we build it in short, fixed phases with the code in your accounts, as described in how we work. If you are weighing a decision like this, you can book a call to talk it through.