Pros

• Has a massive amount of skill expression and allows you to master the champion in multiple ways.
• Is extremely versatile in terms of her role within her team; can be anything from a dedicated split pusher to a full on front to back teamfighting hyper carry.
• Is a true hyper carry champion who is almost impossible to shut down once ahead in the later stages of the game.
• Has the ability to outplay 80% of the champions in top lane with the proper matchup knowledge.
• Is a champion who does 70% magic damage and 30% physical damage which means your team will never be too AD weighted when your mid locks in Zed.

Cons

• By the numbers, needs to draw games out. Loses 60%+ of all games that end before 20 minutes, and does not break even until 25+ minutes.
• High skill expression also translates to high skill floor. She's a difficult champion both mechanically and systematically.
• There is not a lot of build or rune diversity, meaning matchups that are bad are just bad... there's no being creative and getting around it.
• Is a champion who is forced to get in close, but has no hard CC or disengage. You need to pick your fights wisely and never overextend. You're a fighter, sometimes bruiser, but definitely not a tank.

Starting Items

• Doran's blade is your default. Any lane where you will be able to freely take advantage of the passive, will be taking extended trades, or feel you have kill pressure you should be taking Doran's blade.
• Doran's ring is extremely good in lanes where you feel you want to avoid fights and feel that you'll be able to do so.
• Doran's shield on the other hand shows a lot of promise in lanes where you want to avoid fights but feel that your lane opponent will be able to force you into taking them anyways.

It's important to note that both Doran's ring and Doran's shield are significantly better items in ANY situation that you feel you won't be able to take advantage of Doran's blade omnivamp passive.

First Back
Depending on your matchup there are several options you have.

• Leeching Leer is optimal when you have enough gold to one shot it and value you trading power and sustain that it gives you. This also locks you into going rift -> nashors.
• Bramble is an auto buy vs any AD bruisers or fighters every single time, its just too oppressive to pass up.
• Recurve bow is really good against matchups you know you can abuse and rush Nashor's into.
• Blasting wand is a good choice if you're forced to back with less than 1000g.
• Oblivion orb is the superior choice when you need healing reduction but bramble vest isn't the way to go.

Boots
I have the boots ordered in terms of what you should consider.

• Defensive boots are default and safe to go based on lane and team matchup. Pick these boots based off of their PASSIVES, not the armor or MR they give. The auto attack reduction and tenacity are the reasons to buy these boots.
• Lucidity and sorc shoes both have higher winrates and are used in specific situations.
  • Lucidity boots are exceptionally strong when you don't need the tenacity of merc treads or anti auto passive of steelcaps. It gives you a huge power spike with both your q and e cooldowns.
  • Sorc shoes are very, VERY strong in games where you know you won't be forced into bad fights before your core build is complete. If you're in a farming splitpush lane and feel you can drag laning phase out without costing your team the game, sorc shoes are ideal.

Core Items
Not much to say here. For the standard build, these items have to be built. You can take a detour for bramble or oblivion orb, but ideally you're rushing these items. Rush Rift Maker usually, but Nashor's can be a solid rush into matchups you know you can abuse and force early towers out of.

Offensive Items
Each of these items is good in specific situations:

• Deathcap - When you feel that you can afford to build dcap, you should. When dcap is bought, Gwen's winrate SKYROCKETS... but this is assuming there are no factors forcing you to build something like Morello or Bramble vest.
  
• Cosmic drive gives a nice chunk of health, damage, and most importantly a **** load of ability haste. Gwen scales very, very well with coodlown reduction.
  
• Lich bane is an item Gwen actually utilizes extremely well, but should only be built in games where you are going to be forcing the split push rather than looking to take lots of teamfights. It absolutely shreds through turrets and gives you a big chunk of damage in 1v1 scenarios.
  
• Finally, Morello should be built any game where you need to consistently apply grievous wounds and did not go bramble vest.

Once again, these items all have very situational purposes:

• Zhonya's is debatably a "core" item. Any time you can justify the purchase, you should. It just gives you too many options. You can play extremely aggressive in fights, go into stasis, and give your team time to react. You can tower dive and cancel a turret shot. You can survive burst in a gank. It's just too versatile to pass up whenever you can grab it.
  
• Thornmail should be completed later in the game when you go bramble.
  
• Randuin's is EXTREMELY strong as a defensive option as it allows Gwen to stick onto carries for free.
  
• Demonic is considered core by some Gwen players and trash by others. It does give Gwen a much better way to deal with high HP teams, and more than likely should be bought in situations where you feel you'll be playing front to back teamfights or splitpushing against really beefy champions.
  
• Finally, Visage should be your default "well **** I need MR really badly" item. It synergizes perfectly with rift maker, and has all the stats Gwen likes.

The Sunderer Build
Divine Sunderer has a lot of promise. It's an item that gives Gwen a MUCH earlier power spike and allows her to take trades that normally would be suicide. Gwen actually makes a ton of use of AD because of the way she plays. She has only AP scaling, but she's still an auto attack based champion when it comes to trading patterns. Additionally the mythic passive gives both armor pen AND magic pen for some reason, which makes it a really good fit. The problem with the item is that it fundamentally changes the way Gwen plays in trades and early skirmishes, and it doesn't scale as well as just going Rift Maker. I think this is a build 100% worth looking into as it gives Gwen some flexibility in matchups that are generally losing matchups.