Non Drip v's Spray on insulation

As above, ive a hay shed that im converting into a bit of a workshop and Im wondering what are peoples views on the two of the above for the finishing of the roof. It currently has basic galvanise cladding that must be 20 years old and drips water inside the shed. cost wise im working out that the non drip cladding could be done for little over 1000 euro thats me fitting the panels myself. I will be getting a price on the spray on insulation next week. Can this be sprayed onto the galvanise as it is, that is dripping and covered in cobwebs!