Getintent lets you use Report Biulder, which provides flexible adjustment to get the necessary reports with filtering and grouping.
To build an available inventory report, go to the "Reports Builder" tab in the interface and select the "available inventory" dataset:
Available inventory for domains


We can see two columns: domain name and the number of available impressions for it. It's better to include not much than 40% of the numbers in the report while preparing a media plan.