Recently I've been playing tons of Warwick in top lane, because of how broken his ultimate is with Muramana(I won't go into the disgusting details about how much this changes his playstyle), and Black Cleaver DOES NOT stack off of his ultimate because it procs ONLY off of physical damage. Only Warwick's auto attacks will ever proc BC so that is NOT a good item to put on him.
As for how he matches up in top lane it's kind of a mixed bag. I only ever play normals anymore because I hate the current meta, which, in my very honest opinion, is an even more disgusting, twisted clone of last season's meta, so there is no counterpicking beforehand. Warwick does VERY well vs most other top laners mostly because he can sustain very hard and his (only) harass is strong in that lane for the exact same reason that makes Vlad a good top laner. Warwick auto wins against 90% of other champions with weak sustain or no sustain, but gets OWNED by champions who have a 500+ range ability and/or attack speed reducer.
Teemo wrecks Warwick because he can nullify his ultimate with a blind dart and has more movespeed and that constant harass that WW cannot heal through.
Lee Sin SOMETIMES beats Warwick because of how OP Cripple is (haters/flamers take it somewhere else) but luckily the combination of Infinite Duress followed by Hunter's Call's 8 second duration beat that. The problem is that good Lee's will smack you a few times during this then fly away with his magical Safeguard nonsense before that AS buff kicks back in.
Darius unfortunately beats Warwick alot because his full burst shuts down his kit. Darius can easily engage from 500 units away so getting in range to Q him is out of the question. Q'ing him results in often nothing happening because he'll spin that heal out of you at the same range. When Darius DOES engage he usually wins because his Crippling strike wrecks move AND attack speed, so running away (Warwick's only escape) or staying and fighting are both not in Warwick's favor. Even with Wit's End he cannot often sustain through heavy bleed stacks without Hunter's Call. I haven't had a good experience even vs. bad Darius players yet just because of his kit.
I went vs. Nocturne top ONE time (probably the only time ever) and got owned for the same reason Darius often beats me; his kit counters mine so well. Where Warwick sustains by auto attacking single minions a ton with cumulative hits and Q'ing his opponent (Nocturne spellshields it because harassing with WW is easily telegraphed) Nocturne heals a TON with one well-placed hit after auto attacking minions as well. WW heals over time while Nocturne heals it ALL in one fell swoop. Nocturne blocks your only harass and turns it into AS to beat you over the head with and he can also block Infinite Duress. Fortunately, 99% of Nocturne's stick to jungle but the one who top laned wiped the floor with me.
Those are the only top lane champions that have beaten me so far. Everybody else either tries to out DPS my sustain and fails or I trade more damage with my opponent with my Q and one or two auto attacks. I've also found that he CAN mid vs SOME mages (those that counter other mages) since I have been called upon twice recently to switch to mid vs Gragas and Kassadin. Basically, he get's owned by LONG ranged harass and AS reducers as well as the obvious Grievous Wounds, but he stands his ground really well and farms/pushes like a boss. This is coming from a Warwick who HAS to rush a Tear of the Goddess before durability and a Recurve Bow so I'm sure your experiences will be generally better vs most champions.
Anyway, I'm gonna go play Warwick top now because I riled myself up over it. Hope this info helped!