Script to count

Hi,

I would like to have a custom field in my supplier that shows the total number of invoices that it has (Only invoices that have a check box marked should be counted)

I did this with a saved search, but wanting to use these results (the number of invoices per supplier) in a workflow, it doesn’t show me anything since the value is not stored. Do you know if there is any way to make my worflow work using saved search?

I have done some research and found that with a script I could do this too, but honestly I have never made a script and right now I don’t know where to start to create it. Could someone help me or give me ideas where I can start to make the script?

I would greatly appreciate your help.