Tater wrote:
I live in mid wisconsin and am planning on a 40x80' shed and would like
to know what i should be doing for the foundation. I am thinking of
putting a 40x40 concrete slab

You need to explain that. How can you have a 40x80 shed with a 40x40
foundation?

and would like to ensure that frost heave
does not dammage it.

one contractor said to put 2 inches of styrofoam insulation, but he did
not even see the site, so I'd like to know what to prepare before we
get to the styrofoam. the area has a bunch of trees that will be
removed, stumps pulled and etc. I'm wondering if the existing soild can
be used or if i have to get some gravel

You only need gravel to go under the foundation not the slab. Look up
"insulated slab foundations" to deal with frost heaving. You don't need
to excavate really deep that way.

-tg