Annual PO report

I need a report that lets me analyse the purchases made over a period (annual) so that I can report back on budget usage and likely future expenditure.
The supplied Purchase reports give me the total cost associated with a PO but not the item descriptions, but I need a query that gives all the data (PO, vendor, item, quantity, cost per item, cost code, date of purchase).
I haven't worked out the data model to allow me to generate this report, and judging from other custom queries there seems to be inconsistency in naming conventions that makes this difficult - is there any further documentation available, or can someone assist me in producing the required SQL statement please?

Thanks, Kevin