Greenhouses, Sheds and Sun Rooms - Arrow shed on angle foundation - how to fix?

We had someone build our Arrow shed for the side of our home. They did a good job but the sidewalk that is on the side of our home is at a slight angle to drain water away from our home. We didn't really take this into consideration. Once built the shed doors won't open and close without lifting up the side on the down angle that hangs off the sidewalk. This seems to 'square up' the shed.

Anyway I've posted photos of the shed. I know I could put a board under it or something and raise it up but I don't want gaps under the shed as I plan to seal it to the concrete so water doesn't run inside of it. I also do not want to let in tons of bugs, spiders and small animals.

What is the best way to square up this shed without A. Pouring new cement or B. Building an entire foundation for it.

Photos attached:

http://tyandjodi.com/cl/shed1.jpg

http://tyandjodi.com/cl/shed2.jpg

Thanks.

Try just driving a shim under the left (shorter) side under the outside stile. I believe you just have a small deflection in the frame that is causing the binding. I know it will leave a small gap, but you can caulk it or insert a backer rod under it to keep devious pests out.