Delivery precision

I need to create a report for delivery reliablity in purchase line.

.The purpose of “Delivery  Reliability” is to illustrate delivery precision for the worst 15 suppliers, shows delivery performance.

This means The above report will be grouped w.r.t supplier those have Status ‘late’ and sum the Number of PO for that supplier and generate a Report by Biggest No.

could anybody help me out in writing the queries for the report? i have done the design part