What can i use instead of coroplast for a guinea pig c n c cage?

i want to make my piggies a bigger cage b/c all of the cages in the store are too expensive for a girl like me and seeing how they're both males they fight a lot. i love my guineas to death but they chew on everything, you name it so i don't think coroplast is a good option(its also expensive). i've heard cardboard is weak and lenolium is expensive in most stores in the U.S.