Detailed sales and marketing reports

Dears,
first of all, lets congrats ourselves and you for this fascinating software.
second, I noticed that we have good reports but it is general reports.
I tried to make a report represent the biggest buyers in a specific region
but it seems difficult to make !!
also to compare between specific buyers or regions in total sales it can't be done
I tried to design a report but I can't find the documentation describing how to add reports in PHP