Insights · Build vs Buy

Custom software vs SaaS: when each one wins.

A practical decision framework for 1–300 staff organisations. Written by a team that builds both — and recommends each, when it's right.

TL;DR

SaaS wins when your workflow is generic and matches the tool's design. Custom wins when your organisation has real differentiation in how it works, or when you've outgrown the SaaS roadmap. Most growing orgs end up hybrid — SaaS for commodity functions, custom for the bits that matter.

The default is buy. That's a good default.

If you're reading this, someone in your organisation has probably said the words "we should just build it ourselves." That instinct is usually wrong — and we should know, because building software is what we do.

For most jobs, off-the-shelf SaaS is the right answer. It's faster to deploy, lower upfront cost, and maintained by someone else. Email, accounting, payroll, generic CRM, file sharing — there's no good reason to custom-build any of these in 2026. The market has commodity solutions that work.

So when does the default break?

Signs your SaaS stack has stopped working

The problem rarely announces itself. It accumulates. Look for these patterns:

  • Three SaaS tools doing the work of one. Each was bought to solve a specific gap; none of them quite fit; now staff copy data between them.
  • Spreadsheet sprawl alongside the SaaS. The "real" workflow lives in Excel; the SaaS is just a passthrough for some of it. This is the most common sign.
  • "It's on the roadmap." You've raised the feature you need with the vendor. It's been on their roadmap for 18 months. It still isn't there.
  • Workflows shaped by the tool, not the team. You're training new hires on the SaaS's quirks instead of how your organisation actually operates.
  • Reporting requires manual aggregation. Every board meeting starts with someone exporting CSVs and stitching them in Excel.
  • Per-seat pricing that punishes growth. Adding the 50th user costs the same as adding the 5th. You think twice about giving people access they should have.
  • The SaaS owns your data. Exporting it would be a project. Migrating it would be a nightmare. The switching cost shapes your decisions.

Two or three of these on their own aren't a custom-software signal. Five or more means you're paying the cost of misfit software in time, headcount, and missed scale — and you don't see it on a line item.

The case for custom (when it's the right answer)

Custom software isn't about features. It's about fit. The question to ask isn't "could SaaS do this?" — it's "is this part of how our organisation actually differentiates?"

If the answer is yes, then bending your differentiation around someone else's UI is how that differentiation slowly erodes. Custom software is how you encode your way of working into a tool that scales it.

Concrete cases where custom usually wins:

  • Sector-specific workflows. Sports administration, medical reps, sustainability compliance, regulated reporting — generic SaaS doesn't fit, and the sector-specific SaaS is often expensive, narrow, or both.
  • Multi-stakeholder, multi-stage processes. If your work has more than 5 hand-offs between different roles, a generic kanban tool won't hold it.
  • Integration sprawl as a feature, not a bug. You need 6 systems to talk to each other in a specific way. Building a thin custom layer that orchestrates them often beats forcing one of them to become the centre.
  • Data ownership matters. Regulatory, IP, or competitive reasons mean you need full control of how your data is structured and stored.
  • Audit, compliance, and evidence collection. Generic tools rarely capture the exact evidence trail your auditors want. Custom can.
  • You're the product. If your software is what your customers buy (or interact with), it can't be off-the-shelf — your differentiation lives there.

The myth: "custom is more expensive"

This is the most common objection, and it's usually wrong over a 3–5 year horizon. Here's the honest maths:

  • A growing SMB typically spends $50,000–$200,000+ per year on SaaS subscriptions. (Add it up — the number surprises everyone.)
  • A focused custom build for a specific operational workflow is often $80,000–$250,000 one-time, plus modest ongoing hosting + maintenance.
  • Within 2–3 years, the custom build is paying for itself. By year 5, you own an asset; the SaaS subscriptions are a perpetual line item.

The framing changes when you stop comparing one custom build against one SaaS subscription. You're really comparing five SaaS subscriptions stitched together by humans against one purpose-built system. The second is often cheaper, faster to use, and you own it.

The middle path: hybrid (where most growing orgs land)

Custom doesn't mean rebuilding email. The right move for most 1–300 staff orgs is a thoughtful split:

  • Use SaaS for commodity. Email, accounting, payroll, document storage, video calls, generic CRM. There's no winning by custom-building these.
  • Build custom for the parts that matter. The 1–3 workflows where you actually differentiate — that's where custom delivers compounding value.
  • Use thoughtful integration to stitch them. A small custom layer that orchestrates SaaS + your data + your workflow often delivers more value than any standalone tool.

This is the pattern we recommend most often at Stacksy. Custom where it matters, SaaS where it doesn't, and a clear plan for how the two halves talk to each other.

The build-vs-buy decision tree

Five questions, asked in order. Answer them honestly:

  1. Is the function commodity? (email, accounting, generic CRM, file storage) → Buy SaaS. Stop here.
  2. Does this workflow differentiate us in our market? If no → Buy SaaS, accept the gaps. If yes → continue.
  3. Have we tried 2+ SaaS tools and bent them to fit? If no → try another SaaS first. If yes → continue.
  4. Will we still need this workflow in 3+ years? If no → Patch with a SaaS combo and move on. If yes → continue.
  5. Can we name 2–3 specific, measurable outcomes a custom build would deliver? If no → you don't have enough clarity to build yet. Discovery first. If yes → Build custom.

Common mistakes we see

  • Custom-building commodity functions. Building your own CRM when Salesforce or HubSpot would have worked. Never. Don't do this.
  • Building from a wishlist. Customer asks for everything; you build everything; nobody uses it. Custom needs ruthless scope.
  • Hiring contractors to build, with no plan for what happens next. Custom software needs an operator — somebody who owns the roadmap. Without one, it ossifies.
  • Building before you've validated the workflow. If the operations themselves are still being figured out, custom software will encode the wrong shape. Discovery first, build second.
  • Choosing custom because you want to avoid SaaS subscriptions. Cost-avoidance is the wrong reason. Differentiation is the right one.

Where Stacksy fits in

We build software that fits how your organisation actually works — which is the opposite of how most SMB software companies sell. But that doesn't mean we recommend custom every time.

Our Innovation & Efficiency Discovery Program is a no-cost engagement specifically designed to answer this question for your organisation — by spending 3–5 days inside your operation and surfacing where the build-vs-buy line should sit.

Sometimes the output is "stay with your SaaS stack, add this one thing." Sometimes it's "build a custom layer on top of what you have." Occasionally it's "build it custom — here's why." We don't push custom for its own sake.

If you already know you want to build, our Project Scoping Tool takes you through the brief in 10–15 minutes — and we'll come back with a clear path.

Go deeper

Not sure which side of the line you're on?

The Discovery Program is built for exactly this question. No-cost, 3–5 days, led personally by our CIO.

Apply for the Discovery Program →