The template was adjusted as requested

energy_selfconsumption/__manifest__.py

@@ -27,6 +27,7 @@
         "views/res_partner_views.xml",
         "views/distribution_table_views.xml",
         "views/supply_point_assignation_views.xml",
+        "views/custom_paper_format_views.xml",
         "wizards/selfconsumption_import_wizard_views.xml",
         "wizards/distribution_table_import_wizard_views.xml",
         "reports/selfconsumption_reports.xml",

energy_selfconsumption/models/__init__.py

@@ -3,3 +3,4 @@ from . import supply_point
 from . import partner
 from . import distribution_table
 from . import supply_point_assignation
+from . import custom_paper_format

energy_selfconsumption/models/custom_paper_format.py

+from odoo import models, fields
+
+class CustomPaperFormat(models.Model):
+    _inherit = 'report.paperformat'
+
+    custom_format_name = fields.Char('Custom Format Name', required=True)
+    custom_page_width = fields.Float('Custom Page Width')
+    custom_page_height = fields.Float('Custom Page Height')
+    custom_margin_top = fields.Float('Custom Margin Top')
+    custom_margin_bottom = fields.Float('Custom Margin Bottom')
+    custom_margin_left = fields.Float('Custom Margin Left')
+    custom_margin_right = fields.Float('Custom Margin Right')
+    orientation = fields.Char('Orientation')
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