What alternatives to 1/8 plywood?

What alternatives are there to using 1/8 plywood for the roof covering? I am planning on using aluminum over it. I looked around at lumber yards and box stores on my first build, they didn't have it or couldn't/wouldn't get it(due to the fact that they had to buy a whole pallet at a time. Ended up using masonite, I see where it is starting to come apart in a few places where it is exposed at the hatch. Can masonite be sealed with epoxy? The guy I bought the 1/2 plywood from does cabinetry and said that my best bet was to find a cabinet person that using it and has some or is ordering some. Have a couple of cabinet guys that I know that I will check with.