cost reporting docs (#2288)

Co-authored-by: Tamir Kamara <26870601+tamirkamara@users.noreply.github.com>

docs/azure-tre-overview/tre-resources-breakdown.md

@@ -73,4 +73,16 @@ A TRE Workspace will be provisioned in a separate Resource Group along with its
 
 ## Running costs
 
-The exact running costs will depend on the number of workspaces you have deployed, the workspace services you have enabled within them and the Azure Data center region.  You can use the [Azure Pricing Calculator](https://azure.microsoft.com/en-gb/pricing/calculator/) on the above services to get an indicative idea of running costs, or contact your Microsoft representative for further guidance.
+The exact running costs will depend on the number of workspaces you have deployed, the workspace services you have enabled within them and the Azure Data center region. You can use the Azure TRE cost API to get a report of the running costs.
+
+Cost API is based on [Azure Cost Management](https://docs.microsoft.com/en-us/azure/cost-management-billing/) and [TRE Templates azure resource tagging](../tre-workspace-authors/authoring-workspace-templates.md#azure-resources-tagging).
+
+Cost and usage data is typically available in Cost Management within 8-24 hours.
+
+Tags aren't applied to historical data, template authors need to make sure all relavent [Azure resources of a TRE resource are tagged as instructed](../tre-workspace-authors/authoring-workspace-templates.md#azure-resources-tagging).
+
+Cost records might include [multiple currencies](https://azure.microsoft.com/en-us/blog/azure-cost-management-updates-july-2019/#currency) for the same date and TRE resource.
+
+Once cost data becomes available in Cost Management, it will be retained for at least seven years. Only the last 13 months is available from the TRE Cost API and Azure Portal. For historical data before 13 months, please use [Exports](https://docs.microsoft.com/en-us/azure/cost-management-billing/costs/tutorial-export-acm-data?tabs=azure-portal) or the [UsageDetails API](https://docs.microsoft.com/en-us/rest/api/consumption/usage-details/list?tabs=HTTP).
+
+For more information please refer to [Azure Cost Management](https://docs.microsoft.com/en-us/azure/cost-management-billing/costs/understand-cost-mgt-data) and Cost API swagger docs.

docs/tre-workspace-authors/authoring-workspace-templates.md

@@ -111,6 +111,26 @@ The mandatory parameters for User Resources are:
 | `tre_id` | string | Unique ID of for the TRE instance. | `tre-dev-42` |
 | `workspace_id` | string | Unique 4-character long, alphanumeric workspace ID. | `0a9e` |
 
+## Azure Resources Tagging
+
+TRE Cost Reporting is based on Azure tagging to be able to generate cost report for core services, shared services, workspace, workspace services and user resources.
+Templates authors need to make sure that underling Azure resources are tagged with the following tags:
+
+
+| <div style="width:160px">Tag</div> | Value | Applies to |
+| ---------------------------------- | ----- | ---------- |
+| `tre_id` | Unique ID of the TRE instance | All resources of a TRE instance |
+| `tre_core_service_id` | Unique ID of the TRE instance | All TRE core azure resources |
+| `shared_service_id` | The shared service unique ID | Shared Services |
+| `workspace_id` | The workspace unique ID | Workspaces, Workspace Services and User Resources |
+| `workspace_service_id` | The workspace service unique ID | Workspace Services and User Resources |
+| `user_resource_id` | The user resoruce unique ID | User Resources |
+
+!!! Notes
+    Main Azure Container Registry and Storage Account are not be tagged as those resources are used to spin up more than one Azure TRE Instance.
+
+[![Resource tagging example](../assets/resource-tagging-example.png)](../../assets/resource-tagging-example.png)
+
 ## Versioning
 
 Workspace versions are the bundle versions specified in [the metadata](https://porter.sh/author-bundles/#bundle-metadata). The bundle versions should match the image tags in the container registry (see [Publishing workspace bundle](#publishing-workspace-bundle)).