Hello summoners. If you're here looking for builds, you're either bored and want to try something new OR you are new and want to try and get better. In either case, I'm here to introduce you to Tankplank.
Tankplank is a good pick going solo top when your team has a jungler.
I've seen in many games that people don't look at me and give negative comments and that is because they already know about tankplank. It is quite a viable build with several variations. However, I have not seen a tanky GP build on here that has suited my style yet. Here's mine which has worked for many games for me.

EDIT: Gangplank's passive is changed from healing reduction to a stacking slow. This makes him an even more effective chaser and now allows you to better 1v1 critplanks in normal play since they won't reduce your Warmog's/FoN.

Keep in mind that with this build, you aren't going to replace Alistar or Shen. This build more of places you on the Garen side of the tanky dps spectrum. You may not have the defensive skills, but you have a small heal+cleanse which is just as good.
Pros:
Good survivability in comparison to other builds, harder to gib
Hard to gank with movespeed and cleanse
Still dishes out decent dps
Strong 1v1 champ
Unlike other tanks, cannot be ignored/left alone in teamfights

Cons:
Not as much dps as Crit builds
Needs advanced knowledge to 1v2 effectively
Weak cc compared to other tanks

As said in the intro, our goal is to make Gangplank tanky dps.
For this path, you should have little to no deviation from Amor pen marks and Crit damage quintessences.
Seals can be swapped for mana regen for more laning and pushing power. Or take armor/health for more beef.
Glyphs, I really like the flat cooldown for early Parrley farm. If you're really good with last hits, or play on a more advanced level with mana conservation, you can swap them out for MR or something crit oriented.

We must take crit chance and damage in offense to balance the tank slots we're losing to critplank. Advanced ghost should be an obvious choice as well. Exhaust is for 1v1s and saving squishies from those Xin Zhaos. If your team is competent, you can drop it.
Cleanse, Fortify and Clairvoyance are good alternatives that don't require moving up mastery trees to do thir work.
Edit: With the stacking slow passive rather than healing reduction, ignite is now a viable summoner spell. Use your passive to slow and ignite to reduce healing rather than vice versa with exhaust.

The part with the most variation amongst tankplank players are the items.
Grab Regrowth pendant and mana potion or Double Faerie charm with your choice in quantity of health potions. I prefer the pendant route. Take the starting items and preferably take solo top to maximize your freedom over farming. If 1v1, you can harrass with auto attack vs melee or Parrley vs ranged. If 2v1, sit back and Parrley farm.
Try to stay until about 1300 gold to upgrade into double PhiloStone. I go with 3, but if you feel that you want to get started on Warmog's armor earlier, stop at 2.
EDIT: Philostone's passive is unique to itself after post-Season One patch, so only one stone will grant the gold/5, making it fairly trivial to stack them. This also makes the double faerie charm route fairly useless. Grab one stone, one avarice, boots and then start Warmog's - grabbing the Regrowth pendant part early. With the lack of duo/tri stone regen, you may also choose to grab a temporary low cost mana regen item to increase your laning power such as Meki pendant or Chalice.

Warmog's will boost your Force of Nature and Atma's, completing your three piece tank set. This will put you over 3k hp with a good amount of mr and armor. The remaining items will balance you out with damage for endgame. Build defense before damage.
You should be taking treads every game, but if they lack cc or have an AD heavy team go with Tabis.
Final build is Warmog's, Force of Nature, Atma's, IE, TForce, and Shoes.
This build maxed out will put you over 3k hp, over 200 damage, give you about 50% damage reduction of both types, and still have a 60% crit rate.

Only a few points to note here.
If you are having trouble against a harass heavy champ, or are going 2v1 and they are harassing, keep Raise Morale at 1 and shove your non-Parrley points into Remove Scurvy.
You may balance RM and RS however you wish.
At level 6 you should always take your ult. Stop early tower pushes, and help your team get kills.
If you are having no problems with last hitting, you can stop Parrley at 3 to help balance mana and just put it into RM for more harass power.

With the bulky build, you don't need to be afaid to run in first with your team behind you.
Parrley their squishies and run in for auto attacks. Wait for a bit of cc before using RS. If they ccd on you, you already did part of your job.

If their team has Soraka/Alistar or any other team healers, run around and smack their entire team at least once to stop it. If there is only a single support with healing, run and kill them first, switching to dps second.
EDIT: The change on Gangplank's passive in the first post-Season One patch effectively changes his targeting. You should still attempt to kill healers and dps first, BUT you can alternatively attack the melee dps that is still in the back to slow them and prevent them from attacking your team's squishies.

Wait until the teams commit to a fight to ulti, placing it either half on them and half behind them if you have the advantage and they will run. Otherwise try and just hit as many targets as possible.
Don't forget to RM to buff the team. Can be used midfight to strengthen everyone and allow squishies to escape OR used prefight if your team landed a stun to get your melees in range faster.

That's the end! Not too much detail really, I just went over the main points of the build.
The build is quite strong for solo queue and you almost cannot lose if the game goes into the very lategame.
Try it out, leave a comment and tell me how it worked for you.