Amakarevic, the guys have given you great advice, complete with sketches, so I am not going to elaborate, except to say that I concur fully with removing the roof sheathing, and installing it properly. If you don't have one, buy a cat's paw to get the nail heads above the surface, then use a flat bar (often referred to as wonder bars), along with a scrap of wood for a fulcrum, to pull the nails out.
Now, to expand just a bit, I belive that I saw another thread in which you said that you were going to side this shed with cedar shakes, in which case, particularly with shakes, although applicable to other types of siding as well, you will have the same problems, i.e. premature failure of the siding, as you would with shingles on the roof, unless you take similar action with your wall sheathing. Also, your end wall sheathing lends significant support to your gable ends, when installed properly, and with it not meeting on studs, could contribute to a structural failure of the roof.
Lastly, you made another post regarding running electrical to a shed, which I assume is this one. If not already, sooner or later, an inspection is probably going to be requirred. So, whether or not you have pulled a permit for this shed, I will also point out, and I may be wrong, as it is "just a shed", that I believe you need a double top plate on your walls. There may be other issues as well, such as anchors between the walls and foundation, headers, etc., but I cannot see those in these pictures.
So, obviously up to you, but before going too far, you may very well want to consider talking with your local building department, to see what is required, because although it would be a pain to install a second plate at this time, it would certainly be better than seeing it condemned at a later date. And, even if you do have a permit, you may want to talk with them before continuing. In my jurisdiction, as an example, the building department will issue a permit for a shed without me submitting drawings, but they do so on the premise that basic construction techniques will be followed, and if I were to have that shed inspected, I am quite certain that it would not pass.
Just some friendly advice, opinion, or whatever.