Inventory requisition Approval Workflow

Netsuite has an Employee  Purchase order approval workflow, how this does not have any way of checking if the item requested is in invetory, before the PO is raised.

Has anyone implemented or knoe how to implement an employee inventory requistion approval workflow as follows

-- Employee adds required items to (custom?)Inventory requisition form,
-- the form updates /  shows inventory level of items  request for
-- Inventory request is saved / made by Employee,
--  If items in stock, the request is forwarded to Employees Supervisor for Approval, 
-- Inventory is issued by warehouse / inventory staff

-- If However the item or items are not in stock, then the purchase request/approval work flow kicks in, ie