Plaster statue repair?

I have a full-size plaster statue of a woman which is permanently outside. It appears to have been created out of plaster and then coated in something which resembles metal to look at. Over the years and in all weathers, the outer skin has cracked and quite a lot has fallen away. There are also a couple of significant sized holes which will need filling before repair. What is the best way to bring it back to its former glory. I was thinking of fibre glass sheets, rubbing down and then applying something like Hammerite - or is there a better/easier way of tackling this? Any advice much appreciated.