Warwick is a really strong champ early and you should be winning any early jungle fights or skirmishes. This particular build works great for skirmishes and teamfights in particular.
All the mobility granted by Swiftness Boots and WW's passive, combined with extra tenacity and slow resist, makes this build really nice vs kiting and ranged champions.
We're maxing Q, so survavibility in fights is greater than normal (by normal, I mean good).
Try picking the carries in skirmishes/teamfights, unless someone on their team is really strong, then focus them, since we can survive a lot and mess them up with E and R, for our team to get them out of the way (if needed).
P.S. I honestly don't really know how well this build works from behins since most of the games I played with it went pretty well so yeah, when I'll eventually mess things up, I'll update this "guide". Hope you do well with it.