Zed can assassinate just about anyone. I often see people playing him wrong though, either by getting poor items or poor builds. Getting things like crit or attack speed wont really help him, and playing top is just a bad decision all around.
Jungle for Zed is viable, but he mainly shines at mid as a roaming assassin. He can push his lane back to the turret quickly which gives yourself time to look for someone pushed out too far and take them out. Zed scales best with just straight AD and CDR, therefore your best bets are Ionian Boots, BT, Hydra, and LW as his core items.
Also, the ability order I find works the best are: getting Q to rank 3 by level 5, with a point each for W and E, then maxing straight E after your first point in R. At this point you should be around level 12, and can probably go back to finishing Q then W.