Firstly, you why would you take on a project for a client before knowing you can forfill their requirement? Especially with you saying you are new to php (which this application is coded in)!
However with that said…
I have not looked into IP reporting in detail but maybe try looking at the existing report called ‘Sales by client’ as this may point you in the right direction.
Personally I run a variety of custom reports but I do these outside of IP, querying the SQL DB direct and then PDF the result set which is then automatically emailed to managers weekly.
I’m sure I can speak for all the devs here including kovah when I say they would not have time to help with this custom requirement when they have more important things to look at…you may find someone who is willing to do this as paid work, you may want to move this post to the ‘Job Offers’ category otherwise you need to learn php very quickly