1st post, looking for advice

[scook]

One piece is definitely the easiest (as big a piece as you can get into the cabin) but you need to be sure the surface above is flat enough that the plywood will stick to the whole surface. Take a straight edge, a level, aluminum bar stock, etc., and check the surface for flatness so you know what you're dealing with.

When you dry fit the plywood, make some sticks the right length from scrap lumber to wedge in under it and have them handy when you goop it up to hold it firmly up against the overhead.