This report is based off an Average availability report. It gives the average availability of a whole office over the last 30 days. This includes all nodes in Orion and I have it set to group by office. We have a custom property that we use for Location which we use in many reports for grouping. This way devices that don't pull back an snmp location can still be grouped. We have some exclusion filters, so if you use this report make sure to go through and tweak it to fit your needs.
the select fields tab:
Field: City sort: * function: *
Field: Availability sort: * function: AVERAGE
On the Filter results:
Records where City is not empty
Nodes we use for testing etc we don't always put a location/City on them so this filter hides them. That should about do it, enjoy.