Hello,
this is the general view:

This is what's under Condition - Define authorized purchasers:

What I'm doing here is defining a list of people authorized to create purchase orders. It the person is not in the list, the purchase is automatically rejected (that's what's under If no).
Under If yes what am doing is:
Every requester have a specific approver. In the first 4 steps (Condition - If requester is X define varApprover) I check if the default approver is in the office or not (If Out of office message in Outlook is setup). If the approver has an Out of office message, a substitute approver is defined.
Then come the Get record and Start an approval processes:

An in the end the condition based on the response (Approve/Reject)
If the approver approves, the order is released, if the approver rejects, the order is cancelled.
