Availability Check in CNS0

Hello Gurus,

I have a small doubt. My scenario is I purchase for project so as project stock. Whenever I use CNS0 , system is showing materials assigned to project builder CJ20N.

I want availabillity check in CNS0 means if Material is not present in project stock then system should not allow me to save CNS0 delivery.

How to achieve this ?

My second doubt is in the sales order we are assigning WBS element which is billing element. But system is allowing me to assign WBS element which is not a billing element.

So I want some validation or user exit to avoid wrong WBS entry means system shoud give error message that WBS element is not a billing element.

How to achieve both the solutions ?

Regards

Keshav