Creating custom templates in Plesk can be beneficial for automating the setup of websites or applications with specific configurations. Here’s a general guide on how to build custom templates in Plesk:

1. Understand Plesk Templates: Before creating custom templates, familiarize yourself with how Plesk templates work. Plesk uses XML-based templates to define configurations for various components like domains, databases, web servers, and mail servers.

2. Identify Components: Determine which components you want to customize. This could include website settings, PHP configurations, database settings, mail configurations, etc.

3. Create a New Template Directory: You'll want to create a directory to store your custom templates. This directory is typically located in /usr/local/psa/admin/conf/templates/custom/. If it doesn't exist, create it.

4. Copy Default Templates: Start by copying the default templates you want to customize from the /usr/local/psa/admin/conf/templates/default/ directory to your custom directory. This ensures you have a base to work from.

5. Edit XML Files: Open the copied XML files in a text editor. XML files contain instructions for configuring various components. Modify the settings according to your requirements. Be cautious and ensure that the XML syntax remains correct.

6. Test Your Changes: After making changes, it's crucial to test your templates thoroughly. Create new domains or subscriptions using your custom templates to ensure they behave as expected.

7. Debugging: If something doesn't work as expected, review the XML syntax for errors. Plesk also provides logs that can help diagnose any issues. Check the Plesk error logs for any relevant error messages.

8. Deploy: Once you're satisfied with your custom templates, deploy them to your Plesk server. You may need to restart Plesk services or reload configurations for changes to take effect.

9. Backup: Always keep backups of your custom templates and the default templates you modified. This ensures you can revert to a working state if needed.

10. Documentation: Document your custom templates for future reference. Include information about what each template does and any specific configurations it applies.

Remember, customizing templates in Plesk requires careful attention to detail and understanding of the configurations you're modifying. Make sure to test thoroughly in a non-production environment before deploying changes to your live server.