Order reservation

Hi SAP Gurus,

plz tell me "how to reserve the Production Qty at the time of Production order Creation?"

While creating a production order for qty 20 it show me that the 5 qty are in stock in MD04 View.Hence it make a production order of 15 qty.

But i want 20 qty for that perticular Production order with the reservation.

It will help me while create new production order of qty 10.at that time Md04 view show me 20 qty were reserved & 10 qty will be produce against new order.

So How it is possible?

Plz help.

Regds.

Mukesh