Add note about pricing.

Author: rboucher

articles/azure-monitor/platform/metrics-custom-overview.md

@@ -1,11 +1,10 @@
 ---
-title: Custom metrics in Azure Monitor
+title: Custom metrics in Azure Monitor (preview)
 description: Learn about custom metrics in Azure Monitor and how they are modeled.
 author: ancav
 services: azure-monitor
-
 ms.topic: conceptual
-ms.date: 09/09/2019
+ms.date: 04/08/2020
 ms.author: ancav
 ms.subservice: metrics
 ---
@@ -19,7 +18,9 @@ Custom metrics can be sent to Azure Monitor via several methods:
 - Instrument your application by using the Azure Application Insights SDK and send custom telemetry to Azure Monitor. 
 - Install the Windows Azure Diagnostics (WAD) extension on your [Azure VM](collect-custom-metrics-guestos-resource-manager-vm.md), [virtual machine scale set](collect-custom-metrics-guestos-resource-manager-vmss.md), [classic VM](collect-custom-metrics-guestos-vm-classic.md), or [classic Cloud Services](collect-custom-metrics-guestos-vm-cloud-service-classic.md) and send performance counters to Azure Monitor. 
 - Install the [InfluxData Telegraf agent](collect-custom-metrics-linux-telegraf.md) on your Azure Linux VM and send metrics by using the Azure Monitor output plug-in.
-- Send custom metrics [directly to the Azure Monitor REST API](../../azure-monitor/platform/metrics-store-custom-rest-api.md), `https://<azureregion>.monitoring.azure.com/<AzureResourceID>/metrics`.
+- Send custom metrics [directly to the Azure Monitor REST API](../../azure-monitor/platform/metrics-store-custom-rest-api.md), `https://<azureregion>.monitoring.azure.com/<AzureResourceID>/metrics`. T
+
+> [!NOTE] Custom metrics are currently in public preview. Using them will occur additional charges once released for general availability (GA). For more information see [Azure Monitor Pricing](https://azure.microsoft.compricing/details/monitor/). 
 
 When you send custom metrics to Azure Monitor, each data point, or value, reported must include the following information.