material third party

some materials are stocked, but if got a big sales order the

material send to customer directly from vendor,

if it's not a big order (quantity), we send it from stock/warehouse.

(this material can be as third party or stock item).

If I setup item category as BANS, is it possible

to purchase for stock? if yes, What happen

during the order processing ? (use stock or

third party ?)

can anybody help what is the solution ?

Thank you guru