This build is focused on causing as much damage as possible while maintaining a decent rate of survivability.

As with all builds, you have to play the part in order to make them good. Basically you need to play passive until the right moment and do a lot of ganking. Make sure that when you gank you get to use your ult as the initiating attack so that you are not attacked first. If you end up being focused, which will probably happen if you do not play the ninja, then you need to get out of the fight as quickly as possible (i.e. by flashing) even if your hp is high because it will run out fast. Once you are no longer being focused reenter the fight carefully with a hungering strike or a shot with your gunblade and exhausting the enemy with the least hp in range. Of course make sure that when you are ganking that your not alone lol.

Like with any champ, the best time to gank is when an enemy is outnumbered, teammates are healthy, enemy is unaware of your presence, or when they are weak (low hp). When you are ready to gank hide in a bush nearby, if you are in range use your ult to jump on them after your sure your teammates are aware of your ganking intent and are ready. If you are not in range, flash toward toward them from inside the bush and then ult them. If the enemy is not killed by the time they start running then shoot the with your gunblade then exhuast them after the slow ears off and they are not dead.

This warwick is good because it offers you 3 stuns/slows (your ult, the exhaust spell, the guunblade active ability). In the beginning, you will be vulnerable to damage, so be a good ninja, but after you get a decent amount of life steal you can rely on that to keep you alive, just spam your hungering strike in fights and do not be afraid to attack with low health because your life steal will surprise you.

If you want to jungle at start just trade in exhaust for smite.

People will likely ask what the hell you are doing with your build (mainly because of the gunblade) , but you need to just ignore them because they do not know that it works.

Runes and masteries geared toward maximum dps.

Skill sequence and items geared toward surviving while gaining gank potential.

So try it out, practice, and tell me whether or nor it sucks, works for me though.