Do you mean tariff plans for shared hosting, right?
First, Log in to ISPmanager and activate disk quotas
https://doc.ispsystem.com/index.php/Setting_disk_quotas
Then, create a pre-defined user template for every tariff plan and set disk limits.
When a client orders a service in в BILLmanager, ISPmanager will create a new user based on the template corresponding to BILLmanager's tariff plan