Since the lid is slanted quite a bit and because my handyman skills are limited I'm likely going to just buy a board of OSB or plywood, frame it for support and then paint it with weatherproof paint. All I'm trying to do is keep water away from the tank and away from the house. This seems to be my cheapest and easiest option. I'm sure underlayment plus shingles will be the prettiest but it is hard to buy these supplies in small quantities for what will just be a 4'x'8' board and will likely drive my costs up to $100+. Thank you to everyone for your help and if there is a significant flaw in my plan let me know and I'll be sure to listen!