To structure the internal audit checklist, you should follow these steps:

1. **Review Documented Information**: Start by reviewing the relevant ISO documentation to understand the processes and determine compliance requirements.

2. **Define Audit Criteria**: Identify the specific criteria and standards that the audit will assess, such as ISO 14001 clauses.

3. **Create Checklist Items**: Develop specific questions and criteria based on the documents reviewed. Include items that need to be checked during the audit, ensuring alignment with the standard's requirements.

4. **Organize by Department or Process**: Structure the checklist to cover different departments or processes, allowing for a systematic approach to auditing each area.

5. **Include Evidence Requirements**: Specify the type of evidence needed to verify compliance for each checklist item.

6. **Use Tables and Symbols**: Consider using tables to organize information and symbols to highlight positive findings, opportunities for improvement, and nonconformities.

7. **Ensure Comprehensive Coverage**: Make sure the checklist covers all critical elements and requirements to avoid overlooking any important aspects during the audit.