First of all, the items listed above are incomplete, as you will need to build your items depending on what kind of team you face. Since Trundle does not do a whole lot of DPS through his abilities, the following builds make him very tanky, annoying, and hard to kill. It allows him to play the role of DPS/Support/Offtank quite well. Remember, this is an offtank type of build, so if you are looking for a max DPS or jungle guide, this is not for you. Please keep that in mind before you downvote just for the hell of it. I personally do not see Trundle as a true carry and feel there are two viable ways to play him: Offtank/Support and Jungler. If you are looking for a Jungle Guide, Caketown has a great one here: http://www.mobafire.com/league-of-legends/build/trundle-in-the-jungle-35836 ... If you want to jungle and tank, I have a mini-guide at the bottom of this guide that works well if you follow the basic principles and ideas behind Caketown's jungle build. The only difference is, instead of DPS items, you go defensive with of a focus on Armor Magic Resists, as well as health regen, HP, etc. So if you are going to jungle, decide if you want to go the DPS route, like Caketown's Guide or the defensive route as displayed at the bottom of the guide, but be sure to read the Trundle in the Jungle Guide as well, as there is a lot of good info you will need to know in order to play Trundle effectively. If you team already has a jungler and you are forced to lane, or just want to lane, the rest of this guide details a lot of the basic info and build orders that can work well for offtanking.
Below are three item builds, depending on if you are facing a heavy AD/AP/CC or balanced opponents. Remember, however, that the following is just a base guide and you may need to make changes to the item sets or get them in a slightly different order, as the game dictates. If, for instance, the other team is very heavy on CC's and disables, you may get a Banshee's Veil sooner than the sample builds below. Get items that will help you based on your current game and the way things are playing out! Always learn to adapt and buy items based on need. If health is a problem, you may substitute Warmog's Armor for another item, but always plan ahead and pay attention to what the other team is getting for items. If the lack of health, armor, MR, or CC is causing you problems, stray from the sample builds below and get what you need in order to compensate. Games in LoL are always in a constant state of fluctuation and can change quickly, so adaptation and countering your opponents is key in getting the victory.
Total Item cost: 13510
Total item cost: 13380
Balanced AD/AP/ with CC:
Item cost: 14575
Always start out with Doran's Shield and a Health Potion. This will help you hold your lane quite a long time and build up some gold. The health regen is a must, since Trundle's passive is quite lackluster, to say the least and the shield will really help your survivability and staying power in the laning phase. Also, make sure you have a good partner that you can lane well with. Champions with stuns and slows work great to help set up ganks. They also discourage the other team, as they will often be fearful to get too close. On the flip side, try to avoid situations where a melee champ will be the target of a heavy disable and gank situation. Try to stay in lane until you have enough to blue pill back and get your boots and your second item, or at least the armor/MR/health portion of the item. Because you won't have much mana, you'll need to be conservative on the use of your abilities, so try to make sure you have enough mana to kill an enemy champ or keep them from damaging your towers. Keep killing and pushing and try to last hit as much as possible so that you can get the gold you need to build out your full item set. Always be wary of where the enemy is and what they are doing, especially when pushing a tower. Once you have a couple of items and gain some levels, you will want to try to get the golem buff whenever possible.
By early mid game, you should hopefully have some kills and assists and very few deaths, as well as 3-4 of your core items. At this point, you will be moving around and trying to take down your opponents, pushing towers, clearing enemy creeps and grabbing the golem and lizard buffs whenever possible. If you are doing well, you should be quite an annoyance to the other team and pretty hard to kill. Drop your Contaminate (W) skill down as you engage. Remember that Agony (R) gives you the most benefit if you use it on tanks, while Rabid Bite (Q) is your main damage ability and is best used on their high AD opponents. A well placed and well times Pillar of Filth (E) can be a huge benefit, especially in the jungle. While it's not a game changer, for the most part, in the late game, it can be used very effectively to stop runners who try to get away from ganks.
At this point, you'll be trying to finish out your item build and spank your opponents down. You will have to sell your Doran's Shield to get the final item, the Atma's Impaler, but it will help your DPS big time as you finish the game because you will be so hard to kill and have a lot of health and armor/resists. If your team is struggling or having problems and a single death could spell the end, you may opt to get a Guardian Angel as opposed to Atma's Impaler. Remember, buy what you need based on the game you are in, not this guide! Ultimately, with this build, you will be so difficult to deal with that the opponents will be hard pressed to kill you and with all your utility skills, they will curse Trundle the Tank.
Jungle Tank mini-guide:
I've decided to add in another small guide for those of you who may want to Jungle early and then go with a tank build later. As I mentioned earlier in this guide, Caketown has a nice jungle guide found here: http://www.mobafire.com/league-of-legends/build/trundle-in-the-jungle-35836 ... The big hey to being able to successfully jungle is 1)Smite and 2) Madred's Razors/ Wriggle's Lantern. If you want to play jungle tank, you could go with the 20/0/10 masteries that Caketown has, or 1/19/10 (1 point in Plentiful Bounty in offense, drop the 21 point Tenacity mastery in the defense tree and go 2/3 Ardor in defense, add 1 point in Utility Master for the longer neutral monster buff duration). If you go 20/0/10, you will have more DPS than the 1/19/10 build, but will not be a tanky.
If you go this route, you will typically follow Caketown's Jungle Build and guide and start off with Cloth Armor and Health Potionx5. You will jungle until you have enough to get Madred's Razors and work your way up to Wriggle's Lantern. You will use the lantern and Sight Ward to keep vision for your team. Try to at least keep an eye on the Dragon and Baron. You may also try to get wards on your Golem and Lizard and the opponents Golem and Lizard if possible. You goal will be to jungle until you hit level 6 and then help support lanes and keep vision for your team, moving throughout the jungle as time allows to farm gold and buffs. Remember that vision is key though, so make sure you are on the lookout for MIA's and don't get caught up in a jungle gank because you have no vision or awareness.
Here is the basic item build that you will take if you go this route. This assumes a balanced team, so if they are very heavy AD or AP, you may need to change your focus to Armor/MR/Health. Anyways, this is a typical build:
Jungle Tank items: