If you need to generate log files in a format that differs considerably from the manner in which IIS generates log files, you will need to create your own custom logging module. If you create your own logging module, you also have the option of creating a user interface module, and adding reading capabilities to your logging module.
In addition, whether you are using the logging modules bundled with IIS, or creating your own, you will also need to configure IIS logging in the metabase.