Hi,

If you feel that existing reports are not enough and if you need to add custom reports into the system, you have two ways, either you can create a new report or you can make changes inside existing report.

Before going into build custom module, you can check across odoo apps store and see whether there is any module satisfy your requirement, if so you can use it.

For making a new report, you can check the below links:

1. How To Create PDF Report in Odoo

2. How To Create PDF Report in Odoo12 - Part2

3. How To Inherit And Modify Existing PDF Reports in Odoo

4. How To Call A Python Function While Printing PDF Report in Odoo

And if you need to create Excel report, you can check this:

* How To Create Excel/XLS Report in Odoo

Thanks