The Order type will depend on the type of process you are planning to map. can you please elaborate the process you are planning to put in the system. if you use NLAG, you need to create purchase order and accounting document for payment but the stock balance is always zero as it is issued out immediately to the various department.). for further information please refer the link:
SAP – Non Stock Materials (NLAG) - SlideShare
www.slideshare.net/LorenzoLeonelli/sap-non-stock-materials-nlag