You have lots of time, so that's a definite plus. But you're also talking about some expensive tools like a ladder big enough to reach a 40ft roof. That's going to be in the 350-500 neighborhood. Also, I've never worked with concrete roofing tiles, but I've always been told that they're more of an expert job. I'm not sure why, but that seems to be the consensus.
Why not price out the tools, and price out a pro. See if it's even worth it to do yourself after you buy all the specialized equipment. I ran into this with brake fluid swaps on my civic hybrid. It's a crazy procedure that involves a pump inside the engine compartment. If you let it run dry it's crazy expensive replacement. Did it once and asked, what the hell am I doing? Now I take it to the dealer and let them do it for a hundred bucks.