The best practice that the app builder should follow when building out automation is one record change process per object. A record change process is a type of process in Process Builder that starts when a record is created or updated. Having one record change process per object can avoid conflicts or errors when multiple processes try to update the same record at the same time. Option A is incorrect because one workflow rule per object is not a best practice, as workflow rules are considered legacy tools and have limitations compared to Process Builder. Option B is incorrect because one flow per object is not a best practice, as flows are more complex and require more resources than processes. Option C is incorrect because one invocable process per object is not a best practice, as invocable processes are used to invoke other processes from within a process or a flow.