Shed foundation out of square
Assuming that the sides are parallel, since you called it a rhombus, and the framing is attached to the sides of the post as the drawing seems to show:
You can definitely add shim pieces to the posts on the side that is at the top and bottom of your drawing. Depending on the load that the fasteners take, You may need to attach a block of some sort to support the end of the joist, since it won't be properly attached to the long side anymore.

You could also frame the walls square, and have them overhang the short corner.

Ideally, you should not finish paying the builder until he fixes it.