I support what RTN11 has posted. The flight manual contains a checklist, that is your "official" reference for flying the aircraft. Perhaps the aircraft operator has a few additional checks to be made, which are relevant to the local operation, or additional equipment in the aircraft. That might be a local operating procedure.
Also be aware that the aircraft could have applicable Flight Manual Supplements, for additional equipment, and those FMS' could also contain checklists which you must follow. An example of this would be a Cessna modified to have amphibious floats, will have additional checklist items which are not in the basic FM, and are vital for flight safety.
However, resist long multi page home made "checklists" which differ, or attempt to expand on what the manufacturer has written about operating the plane. Ultimately, when you are flying the aircraft, you are solely responsible to assure that it is operated in accordance with the manufacturer's recommended practices. If you are using a "checklist" other than that provided by the aircraft manufacturer, how can you be sure you are doing that?
As said, a checklist is a mind bumper to help you confirm that you have done, what should have been done. The "Emergency Procedures" and "Normal Procedures" sections of the flight manual tell you how the plane is to be operated. Those sections will contain checklists, as a part of the procedures, and those are the authoritative checklists.
When the manufacturer of the aircraft prepares a checklist in the flight manual, it gets approved by the authority (FAA, for example). Its not a template for someone else to build upon for a thicker checklist - it is the checklist for the aircraft in that configuration. Unless another company (perhaps who holds an STC for that aircraft) gets an FMS checklist approved for that aircraft, the flight manual holds your only approved checklist.