Patio extension- Soffit

About to start a patio extension for my house. I have fascia brackets that need to attach into the roof. Is there any reason I can't just take the soffit off and go from underneath rather than have to remove roofing sheets to go from the top. It's a 2015 built house. My logic is there won't be any risk of me stuffing the reinstall of the colorbond roofing leading to leaks. Plus I'm scared of heights hahah