Every growing business eventually faces the same software decision: find an existing product that handles this need, or build something custom. The decision is harder than it looks because both choices come with costs that are not fully visible at the time the decision is made.
The SaaS industry has made "buy" the default answer for many businesses, and for good reasons. Established platforms handle infrastructure, security, updates, and compliance. The upfront cost is low. You can be operational within hours. For most business processes - email, accounting, project management, customer support - this is the right call and the case is clear.
But "buy" is not universally right, and the cost of choosing the wrong direction is high in both cases. Building something you should have bought wastes development resources on solved problems. Buying something that does not fit your process costs ongoing subscription fees, workaround maintenance, and the organizational friction of conforming your operations to software designed for someone else's needs.
What SaaS Gets Right
The case for buying is strongest when the problem you are solving is common, the competitive differentiation is not in how you solve this problem, and the data ownership requirements are standard.
Accounting software is the clearest example. The process of recording transactions, generating financial statements, and filing taxes is not where any business gains competitive advantage. The software that handles it does not need to be unique. It needs to be reliable, compliant, and maintained - which commercial accounting platforms handle at a fraction of what it would cost to build and maintain equivalent functionality.
The same logic applies to many categories: email marketing, scheduling and booking, customer support ticketing, HR and payroll, video conferencing. These are infrastructure tools. The value is in using them, not in owning them.
SaaS platforms also handle concerns that are genuinely expensive to get right: security patching, uptime infrastructure, compliance certifications like SOC 2 and HIPAA, and mobile applications. When a SaaS vendor handles these, your team does not have to. That is a meaningful cost reduction, particularly for smaller teams.
Photo by Mizuno K on Pexels
When Buying Creates Problems
The case for buying weakens when the software needs to reflect your specific business logic, your competitive advantage lives in how you do the thing the software manages, or the integration requirements become so complex that you have effectively built a system around the SaaS product.
Workflow mismatch: Generic SaaS products are designed for the median user. If your process deviates significantly from what the product was designed for, you spend ongoing energy working around the product rather than using it. These workarounds accumulate. After 3 years of workarounds, teams often have a patchwork of custom logic layered on top of an off-the-shelf platform that is harder to maintain than custom software would have been.
Vendor lock-in and data ownership: When critical business data lives in a third-party system, extracting it requires the vendor's cooperation. Export formats change. APIs get deprecated. Companies get acquired or shut down. The more critical the data, the more seriously you should consider where it lives and what your options are if the vendor relationship ends.
Integration sprawl: Businesses that connect 8-12 SaaS tools via integrations often discover that they have built the functional equivalent of a custom system - but without the architectural coherence of one. Each integration is a potential failure point. Each vendor API update potentially breaks something. The Zapier or Make automation that handles a critical workflow is just a custom system described in a different language.
Subscription cost at scale: SaaS pricing typically scales with usage - per-seat, per-contact, per-API-call. At low volumes, this is cost-effective. At high volumes, the math can reverse dramatically. A tool that costs $200/month with 50 users may cost $3,000/month with 500 users, while a custom solution has fixed infrastructure costs regardless of user count.
The Real Costs of Building
Building custom software is not just a one-time development expense. Understanding the full cost profile is essential for an honest comparison.
Initial development: The upfront build cost is the most visible number, but it is typically the smallest component of the total cost of ownership over a 5-year horizon. Initial development includes requirements work, architecture, implementation, testing, and deployment.
Ongoing maintenance: Software requires maintenance regardless of how well it was built. Dependency updates, security patches, bug fixes, and minor feature additions all require developer time. A reasonable estimate is 15-20 percent of the initial build cost per year in maintenance. Factor this into any build-vs-buy comparison.
Infrastructure: Custom software needs hosting, monitoring, backup, and reliability infrastructure. Cloud infrastructure costs are manageable and predictable, but they need to be included in the cost comparison.
Enhancement work: Over time, your requirements will change and the software needs to change with them. Custom software gives you complete flexibility to implement enhancements, but each enhancement requires development resources. SaaS products often add features on their own roadmap, which may or may not align with your needs.
The build cost estimate for a business application typically ranges from $30,000 for a simple internal tool to $250,000+ for a complex multi-user system with integrations. These numbers scare some businesses away from building when they should not - but only if the comparison is to the SaaS product's monthly subscription cost in year one, not to the total 5-year cost including subscription growth, workaround maintenance, and integration overhead.
When Building Makes Sense
Custom software is the right investment when the process it supports is a genuine differentiator, the volume will make per-unit SaaS pricing expensive, the workflow is unique enough that no SaaS product fits without significant compromise, or the data security requirements rule out third-party storage.
Manufacturing operations management, complex pricing and quoting systems, specialized industry workflows, proprietary analytics and reporting, and customer-facing tools that reflect your unique service delivery are common categories where custom development produces clear ROI.
The key signal is: would a competitor who used the same SaaS tool as you have the same capability? If yes, the software is not a differentiator. If no - if your process requires something the SaaS tool cannot do - that is the case for custom.
Photo by Digital Buggu on Pexels
A Framework for the Decision
A structured comparison covers six dimensions:
- Process fit: How well does the available SaaS product fit your actual workflow? Rate 1-5, where 5 is exact fit and 1 is requires significant workarounds.
- 5-year cost: Total cost of SaaS (subscription growth, integration maintenance, workaround overhead) vs total cost of build (development, maintenance, infrastructure). This number is almost always more favorable to building than the year-one comparison.
- Data ownership requirements: Do regulatory, compliance, or competitive sensitivity requirements affect where data can be stored?
- Integration requirements: How many integrations does each option require, and who maintains them?
- Competitive advantage: Does how you do this thing differentiate your business?
- Organizational capacity: Does your team have the capacity to manage a custom software development process and ongoing vendor relationship?
No single dimension determines the answer. The decision is a weighted evaluation of all six.
The Hidden Cost of SaaS Integration Sprawl
One cost that rarely appears in buy-side analyses is the cost of connecting SaaS products to each other. Most businesses use 8-15 SaaS tools in their operations. These tools need to share data - contacts, orders, support tickets, invoices. Every connection is a potential maintenance burden.
Zapier and Make are popular integration tools that handle many of these connections without code. They work well for simple, linear workflows. But as workflows grow more complex - with conditional logic, error handling, multi-step transformations, and high request volumes - these tools become expensive, brittle, and hard to debug when something goes wrong.
The cost of integration maintenance is frequently invisible in the original buy decision. "We will connect it to Salesforce via Zapier" sounds simple and low-cost. Two years later, that Zapier automation has grown to 40 steps, breaks every time either connected system updates its API, and requires a developer to diagnose failures that business users cannot understand. That maintenance cost belongs in the build-vs-buy analysis.
Custom software that handles data natively - with a database that other internal tools query directly - eliminates most integration overhead. There are no API calls between systems for data that lives in the same database. This architectural advantage does not show up in year-one cost comparisons but compounds significantly over 3-5 years.
How to Get This Right
The most common mistakes in build-vs-buy decisions are comparing year-one costs only, underestimating SaaS integration complexity, and overestimating custom build costs by using vendor estimates without getting a second opinion.
137Foundry regularly helps businesses work through this evaluation honestly - which sometimes means recommending a SaaS product and sometimes means scoping a custom build. The goal is the right answer for the business, not the answer that maximizes any particular engagement. The SaaS replacement services page covers cases where businesses have made the shift from commercial software to custom and what drove those decisions.
For methodology on software cost estimation, the Project Management Institute's resources at pmi.org cover estimation approaches. Gartner's research on SaaS total cost of ownership at gartner.com/en/information-technology provides enterprise benchmarks that are useful as reference points even for smaller businesses. The Thoughtworks Technology Radar at thoughtworks.com/radar covers which approaches the broader industry is using, which provides useful context for these decisions.
The 137Foundry about page covers our broader approach to software consulting and development if you want to understand how we approach these evaluations in practice.