Never had any issues with rodents. We got city sewer rats, talk about honking big things! We have three resin sheds and they never bothered them but they sure did chew the heck out of the neighbor's wooden shed LOL! Next door neighbor across the street also have a resin shed, not a bite.
The only time the rats would do is to chew on the bottom of the foundation, which it was wood and I didn't layered with hardware wire. (my fault!).
Rat poison took care of them. I could not believe how many piebald colored rats I saw than the ugly brownish gray rats I've seen.
Why not metal....well look at the Morton buildings.....they are made of steel and I bet if you can "copy cat" the way they insulate the walls, vents and all that stuff they do, I bet you can make a go of it! However it will cost you more in the long run.