[Strawbale] foundation help

[I.A. Greenberg]

Hi,
I'm interested in building a straw bail studio/playroom in my backyard, but there are lots of trees.  I have a clear space for the small structure, but don't want the foundation to kill the roots of the beautiful maple that it will sit under.  For a small structure, how far down does the foundation have to go, and are there types of foundations that are more on the ground level?  I live in CT where the ground gets cold!
Any websites or resources you could suggest?  Or advice?
Thanks!
izzi