Need help with venting

Hello I’m in need of some guidance. I’ve had my cieling leak on me for 3 years and I think it’s due to the fact that I have no air gap nor any venting. A lot of moisture under my poly and water just keeps on dripping. I am going to replace the roof with metal. It currently has corigated steel but I bought some new sheets. How do I go about doing this the second time but doing it right. I’ve removed the insulation because it was wet. I’ve attached a couple photos Please any help would be great.