Hi MD,
About extractors 2LIS_02_HDR, 2LIS_02_ITM and 2LIS_02_SCL. What kind of standard reports are "usually" used by clients?
2LIS_02_HDR - ECC table EKKO - this will give mainly header level information of purchase Order
2LIS_02_ITM - ECC table EKPO - this will give mainly line item level information of Purchase Order
2LIS_02_SCL - ECC table EKKN - this will give mainly schedule line level information of Purchase Order
Generally Purchasing reports are very much standard like KF wise amount and quantity say PO amount and PO quantity.
SAP provided LO cockpit for Purchasing/Sales Order, so above datasources are also well integrated and as mentioned can not only hold the specified ECC table but also refer other tables too.
go through different threads as you will find many good purchasing discussion as well as articles though, although go thru http://help.sap.com/saphelp_sm32/helpdata/en/8d/bc383fe58d5900e10000000a114084/frameset.htmhttp://help.sap.com/saphelp_sm32/helpdata/en/8d/bc383fe58d5900e10000000a114084/frameset.htm
Do as self question (what may your client can ask you, and try to get it answered using scn and Google) if still you have specific question, don't forget to mark it as new question on scn.
Don't worry, you will do it 
Also suggestion : mark your thread as question, this will attract people to answer and gain points, so you will get much quiker and more reply
Thank-You.
Regards,
VB