Store procedure for PO

Hi friends ,

I need a store procedure for purchase order .

For example:

Purchase order numbering series is CAP-14 and they choose the Business partners then they choose item . if it is(Numbering series) cap -14 that item is item group should be also capital group (item group code 116). if it is choose other item group document should not be add . is it possible in sap ???? give that sp how do i create