Custom software vs SaaS: an honest build-vs-buy guide for growing businesses
Most businesses make one of the biggest technology decisions they will ever make on gut feel.
Do you buy an off-the-shelf SaaS product, or do you build something made for you? The conversation usually turns into a debate about cost, then speed, then risk, and ends with a choice nobody can quite justify six months later.
This guide gives you a framework instead. We build custom software for a living, so we have a horse in this race. But SaaS is often the right answer, and we will tell you when it is. The goal here is a clear-headed decision, not a sales pitch.
SaaS and custom software, quickly defined
SaaS is cloud software you rent on a subscription. Think Microsoft 365, Salesforce or Xero. It is ready to use, updated for you, and available anywhere.
Custom software is built for your business and your workflows. You own it, it fits how you actually work, and it does not force you to bend your process to fit someone else’s product.
Both have their place. The rest of this guide is about working out which place is yours.
The comparison at a glance
- Speed to deploy: SaaS is immediate. Custom takes weeks to months.
- Upfront cost: SaaS is low. Custom is higher.
- 5-year cost of ownership: SaaS rises with every seat. Custom is front-loaded, then flattens.
- Customisation: SaaS is limited to the feature set. Custom is whatever you need.
- Data ownership: SaaS holds it on the vendor’s servers. With custom, the data is yours.
- Vendor lock-in: High with SaaS. None with custom.
- Integration: SaaS depends on the vendor’s APIs. Custom is built to fit your stack.
- AI capability: SaaS gives you whatever the vendor ships. Custom can be trained on your own data.
- Best-fit stage: SaaS suits early or standard operations. Custom suits established or specialised ones.
The real cost picture
SaaS looks cheaper because you only see the monthly bill. Custom software looks expensive because you see the whole cost upfront. Neither number tells you the truth on its own.
The honest comparison is total cost of ownership over three to five years.
Here is the pattern, using illustrative figures. Say a SaaS tool costs £40 per user per month. For 10 people that is £4,800 a year. Manageable. But you grow. At 40 people it is £19,200 a year, every year, rising as you add seats and as the vendor raises prices. Over five years you have spent the best part of £100,000 and you own nothing.
A custom build for the same job might cost more to start, then far less to run. The spend is front-loaded, then it flattens. At some point the two lines cross, and that point comes sooner than most people expect once headcount climbs.
The rule is simple. SaaS is cheaper until it isn’t. The question is whether you will reach the crossover, and how fast.
Build vs buy: the checklist
Run your decision through these five questions.
- Is this process core to how you compete, or is it just plumbing?
- Does the off-the-shelf option force you to change how you work?
- How many seats will you be paying for in three years?
- Do you need to own the data and control the roadmap?
- Is there a tool that already does 90% of this well?
The pattern that emerges is usually clear. Buy for commodity. Build for your edge.
If a process is standard and a good tool already exists, buy it and move on. If a process is the thing that makes you money and no product fits it properly, that is where a custom build pays for itself.
The third option most guides ignore: hybrid
The build-vs-buy framing suggests you have to pick one. You don’t.
Most mature businesses run a mix. SaaS for the standard work, such as email, accounting and CRM. Custom software for the part that actually sets them apart, stitched into the tools they already use.
This is usually the smart answer. You get speed and low cost where it doesn’t matter, and control and fit where it does. It is also where we spend most of our time, connecting the software a business already relies on to something purpose-built around its real workflow.
What Custom Software as a Service (CSaaS) means
There is a middle path on cost, too.
Custom Software as a Service gives you ongoing access to development, support and improvement without hiring an in-house team. You get software built for you, maintained and evolved over time, on a model that spreads the cost rather than demanding it all at once.
It suits businesses that want the fit of custom software without the fixed overhead of a permanent development team.
The AI question
AI now sits inside this decision, whether you plan for it or not.
Off-the-shelf tools bolt AI features onto a product built for everyone. They are useful, and they improve on their own schedule, not yours. Custom software lets you train AI on your own data and your own processes, so it works the way your business actually works rather than the way an average business might.
If AI is going to be a real advantage for you rather than a checkbox, that usually points towards custom.
A business that outgrew off-the-shelf
Jeremy Shingler had run Shingler Homes for more than 20 years, and for most of that time he had been hunting for software to run the business on. He wanted one system for the whole new-build journey, from the first sales lead and show-home visit through to snagging and aftercare.
The off-the-shelf market let him down. The comprehensive systems were built for large national housebuilders and priced for them too. Nothing affordable did what an average home builder actually needed. So in 2018 he came to us and asked us to build it.
We studied how the business really worked, then built Housebuilder Pro around it. It is a paperless, cloud-based platform that manages every stage from plot to the end of the 10-year warranty: sales progression, customer choices, inspection tracking, handovers and aftercare, all in one place.
It fit the work so well that Shingler ran it internally for over a year, then asked us to turn it into a product other builders could use. Today Housebuilder Pro is used by more than 50 housebuilders across Great Britain and Northern Ireland.
That is the difference custom makes. No product fit the way this business worked, so we built one that did, and it grew into an asset in its own right. See the Housebuilder Pro project.
SaaS is the right call when you are early stage and still finding your feet, when your needs are standard and well served by existing tools, when budget is tight and cash flow matters more than ownership, or when you are testing a market and need to move now.
In those cases, buy the tool and build later if you outgrow it. That is a perfectly good plan, and a common one.
Frequently asked questions
Is custom software more expensive than SaaS?
Upfront, yes. Over three to five years, often not, especially as your user count grows. The right comparison is total cost of ownership, not the first invoice.
Can you mix SaaS and custom software?
Yes, and most established businesses do. SaaS for standard functions, custom for the parts that set you apart. This hybrid approach is usually the most sensible route.
How long does a custom build take?
It depends on scope, but expect weeks for something focused and months for a larger platform. A good partner will phase it so you see value early rather than waiting for everything at once.
Who owns the code with custom software?
You do. That includes the code, the data and the roadmap. With SaaS, you are licensing access, not owning the product.
What is Custom Software as a Service (CSaaS)?
Software built for your business, then maintained and improved over time on a subscription-style model, without you hiring an in-house development team.
When should a business switch from SaaS to custom?
When the tool starts dictating how you work, when per-seat costs climb faster than the value you get, or when the process it handles has become central to how you compete.
Not sure which way to go?
That is the conversation we have most weeks. Tell us what you are wrestling with and we will give you a straight answer, even if the answer is “stick with what you’ve got.”