Three quarter inch douglas fir plywood is fairly rot resistant. Depends on availability and price in your part of the country.

You may have an even equal or greater rot resistance type of plywood available there as well. Make sure it is exterior grade stamped as that means waterprrof glue usually. No waterproof glued plywoods can delaminate as you probably are well aware.

I was surprised at the specis of trees used in plywoods only a couple of thousand miles south of where I live. We never had access to many of those specis of lumber or plywood up here.

Ask if they have any damaged sheets where you shop as one corner even seriously damaged is inconsequental to your needs.