custom record with expense and item sublist like purchase order record

Is it possible to make a custom record that has the same sublists that are in the Purchase Order record? Expense and Items? I'm trying to make an approval process for when changes are made to a purchase order. I thought I could have the user make changes to a custom record and then if it is approved I can move those changes over to the purchase order. Another thought I had was if you could edit a purchase order and then rollback to the last saved version somehow if the changes made are not approved?

Initially I was going to make a copy of the purchase order, update the original purchase order based on changes made to the copy, and then delete the copy of the purchase order. However, that seems very messy and then there will be duplicate purchase orders out there until the approval process is completed.