When to buy
Your need is mainstream. Off-the-shelf SaaS tools cover 80%+ of what you'd build. Volume is below the SaaS pricing tier where it gets dumb (typically when you'd pay > £2k/month for a single tool). Your team will use the tool weekly, not just for a one-off.
When to build
Off-the-shelf forces a workflow you can't actually adopt. Volume is high enough that SaaS pricing punishes scale. The workflow gives you competitive edge — i.e., your competitors don't have it, and you don't want them to.
The middle
Most real situations sit in the middle. Buy the parts that are commodity (lead capture forms, scheduling, CRM). Build the parts that are differentiating (your specific qualification logic, your routing rules, your ICP scoring).
— Arora