"Should we build or buy?" is the wrong first question. The right one is: is this process a source of differentiation, or is it table stakes?
Buy the table stakes
Attendance, payroll, CRM, and ERP are solved problems. A well-built product gets you running in days and improves without your engineering time. Customising these to death is where budgets go to die.
Build the differentiation
The workflow that makes your business unusual — the thing customers notice — is worth owning. That is where a bespoke build pays back, because off-the-shelf tools force you to look like everyone else.
The pragmatic middle
Often the answer is both: deploy SaaS for the commodity operations, and build a thin, custom automation layer on top for the parts that are genuinely yours.