Hi Praveen,
You need to have the Open PO count in your report. Is that what is required here.
If yes ,then first create an CKF to get the document count using exception aggregation.Then using this you can create an RKF also including delivery status indicator.
For doing this you need to have document number and delivery status in the cube .You can mark it as line item dimension to avoid any performance issues.
hope it helps.
thanks