I am going to put up a 12 X 20 Building to house my tractor and some other stuff. I finally found a ready made shed with a high enough door. Anyway I can get the concrete cheap enough ($500) for just a slab. Do I need a rat wall (18" recommended)? I am not sure if this size shed will be susceptible if critters burrough under it. We do have chipmunks and other burroughing critters in the area. I am probably going to be selling the property in a couple of years. Thanks.