How to Prepare a materials purchase budget

When we have to prepare a material purchase budget Generally u follow this:

Sales xxx
ADD closing stock xxx
LESS opening stoc (xxx)

---

Production xxx

BUT I FOUND IT ALSO LIKE THIS:

material purchases budget xxx
LESS closing raw material stock (xxx)
ADD opening raw material stock xxx

---

material usage budget xxx

While in the first exampe we ADD CLOSING stock , in the second one we deduct them..
Can someone explain me the difference and also where can I find material to learn more about them?