Custom system or SaaS: when each one pays off
A guide for small business owners: when SaaS is enough, when a custom system pays off, and how to combine the two.
I often get a question that sounds technical but is about business: "is it better to subscribe to a SaaS or build a system from scratch?"
SaaS is a system you use online and pay for by subscription. The answer, as with much of software engineering, is "it depends." But that is not helpful without criteria. This is how I guide clients, based on systems I have built both ways.
Rule 1: start with SaaS until the process hurts
If you are starting out and your process fits in a SaaS, use it. Seriously.
You get a working system in hours, with automatic updates, no server to maintain, and no developer to hire. You pay a monthly subscription and find out whether your process really needs a custom system before investing in one.
You do not need to leave SaaS because it has flaws. Leave when the cost of working around a limit exceeds the cost of building. If you spend two hours a day exporting spreadsheets from the SaaS and importing them into another system, the math has already flipped.
Rule 2: go custom when a business rule gives you an edge
SaaS handles common processes well. It does not handle what makes your business different.
I built a multi-tenant SaaS platform for electronic real-estate registration. Multi-tenant means several clients use the platform, each with their own data. The business rule was the client's competitive advantage. In Brazil, real-estate registration involves notaries, banks, buyers, sellers, and the National Registry Operator. Each has its own legal requirements, regulatory deadlines, and communication formats. No generic SaaS covers all of that.
If no option on the market supports the rule that brings money to your business, building may be the only option. In that case, it is an investment, not a cost.
Rule 3: go custom when integration is the product
If your system's value is connecting tools that were not made to work together, SaaS may solve the wrong part.
I built a multi-tenant SOAP integration gateway that connected dozens of clients to a national registry system. Each client had different credentials and data formats. CRUD was a small part. CRUD means the basic actions to create, read, update, and delete records. The product was reliable integration, with a pool of tokens, encrypted credentials, and background workers. They processed 13 message types at once. No SaaS offers that as a service because the hard part depends on that field's rules.
Rule 4: go custom when the per-user cost exceeds a small team's cost
SaaS often charges per user. With three people, the price may fit the budget. With 200, the per-user cost grows quickly.
A custom system with 200 users costs the same as one with 3. The cost is development and infrastructure, not a license per person. Compare the yearly SaaS cost multiplied by the user count with the build cost plus yearly maintenance. If the second total is lower, the system pays for itself in months.
The middle ground almost nobody considers
Between using only SaaS and building everything from scratch, there is another option: use SaaS as the core and build custom integrations at the edges.
Keep SaaS for what it does well, such as CRM, email marketing, and accounting. Then build the layer that connects these tools to each other and to your business's specific rules. CRM is a system for managing customer relationships. This approach costs a fraction of a complete system but works as one connected set.
This model worked in the business platforms I built. Finance exchanged information with academics, academics with sales, and sales with the payment gateway. Each module used the right tool, and a custom layer connected them all.
Where it breaks
A custom system without documentation becomes technical debt with interest. Technical debt is extra work caused by choices that make future changes harder. If only one person knows how it all works, the system depends on that person's availability. Build cost includes documentation, without exception.
A SaaS without a clear SLA also brings risk. An SLA is an agreement that sets the service level, such as expected availability. If the service goes down for eight hours on a business day, your business stops too. Read the SLA before signing. If there is none, treat the service as something that could disappear.
If you are unsure whether to choose SaaS or a custom system, tell me about your situation. I will help you do the math with your business numbers, not portfolio numbers.