SaaS is a delivery model. Custom is an ownership model. Do not confuse them.
You can subscribe to someone else’s product, build software only you run, or sell a product to many customers. Those are three different projects.
Three decisions hiding in one acronym
SaaS, as a buying decision, means you pay a vendor to run software for many customers. You get a tenant in their world. Your leverage is configuration, their API, and the threat of leaving. Your constraint is their data model, their uptime, their subprocessors, and their roadmap. This is the right move when the job is standard: email, payroll in many markets, a well-understood CRM for a simple motion.
Say which of the three you mean
Subscribe, build for ourselves, or sell to many tenants. Include the object and the first buyer or user. We will answer in those terms.