Welcome to the Bunnings Workshop community. It's fabulous to have you join us, and thank you for sharing your question about your metal fascia.
If you are confident of the positions of the timber rafters on your roof, I suggest using a Multi-Tool in combination with the Diablo 85mm Wood / Metal Multi-Tool Segment Cutting Blade. The Multi-Tool Segment Cutting Blade is designed with durability in mind to cut through hardwood, non-ferrous metals and laminate panels for a variety of jobs. Please make sure to wear safety goggles and gloves when operating this tool.
Let me tag our experienced members @Noyade, @TedBear and @Baggs for their recommendations on cutting metal fascia.
If you have any other questions you need help with, please let us know.