Why do you think it is leaning like this?
If you've not been playing any Sam Cooke lately, then you have not braced the walls off the roof properly. And the lack of sheathing.
You need to remove any screws/nails joining the roof to the walls, and then with a big timber on an angle between the ground and the top of the wall, force the top of the wall back. Then refix the wall to the roof.