As a reseller of AWS products, I want to use AWS tools to calculate bills for my end users.
As a reseller, it's a best practice to design your own specialized reporting and invoicing structures that match your business needs.
You can use the AWS Cost and Usage report to help calculate bills for end users. It's a best practice to use cost allocation tags to identify the source of your costs.
When you calculate bills for your end customers, make sure to use unblended rates. Blended rates are averages and aren't meant to reflect actual billed rates.
AWS Organizations
Consolidated billing for AWS Organizations