Hi Ignacio,
Thank you for posting your concern.
However, unfortunately, generating custom reports are currently not supported in the AdWords API. You may refer to this guide to see the all available report types in the AdWords API.
For Predefined reports, you may download several types of equivalent reports via the AdWords API. Please refer to this guide as it maps the concepts and naming conventions for reports in the Google Ads UI to the comparable AdWords API reports.
Also, the code samples provided in this link are examples of common reporting functions using the AdWords API (also available for other languages).
Please let me know if you have further clarifications.
Regards,
Hiroyuki
Google Ads API Team