reply to bookman
Re: Shoring up sagging shed floor Its too bad they did such a poor job installing the shed.
Are you sure the floor joist are 4x6 I assume you meant 2x6, having 4 means they are on 2 foot centers. That is not much of a floor.
Tearing out the floor is one possibility but the plywood may be glued to the joists.
My first choice would be to call them back and have it set properly.
If that is not possible have you thought about renting some jacks, jacking the shed up to give you work space?