Almost every team should have a tank and the difference between a good tank and a bad tank will win or loose the game.

In this guide I aim to point out the differences between tanks and the importance of choosing the correct tank for your team.

There are more tanks that are viable choices in 5v5 games but I believe these three excel the most in there specific role and will have the most effect on the outcome of the game

The items list for each build are obviously incomplete and this is due to the nature of building a tank, I do like to have my start items almost set in stone but after them it entirely depends on the other team.

Well put simply as a tank its your job to give your high damage dealers enough time alive so they can kill everyone else.

To do this you need stuns/taunts/silences and slows to protect your team and enough health/armour/resist so you can happily sit in that really painful spot between your team and there team.

Stuns
A stun should be used to disrupt channelling ults as this will negate serious damage output from the other team.
Stuns can also be used to disable high damage dealers during the fight or to initiate with some one who over extends at the start.
At the end of the fight stuns can be used to ensure more of your team escape or help in to chase the other team down.

Taunts
Taunts have 1 main purpose but several applications. A taunt will for a while at least force your targets to attack you. Taunts are most effective against hand to hand combat champions as it will force them to follow you whilst ranged champs will just redirect there fire.
Taunts are highly effective early game under turrets as you will get additional damage from the turret and during team fights they are invaluable due to being able to redirect some ones fire away from a weak char onto you.

Silences
Whilst none of the champs listed have silences they can totally disable characters that rely on there ability's such as casters a well timed silence can completely turn a team fight around.

Slows
Slows are used during chases and they do exactly what they say of the tin they slow the target. This basically has 2 applications, either letting a team mate catch up with some one or letting them flee from some one. This ability can be easily added to any tank with Frozen Mallet and will often be the reason you get additional kills after a team fight.

Role
your main role on Amumu is to destroy team fights by making the entire team stand still hopelessly for 2 seconds whilst you and your team deal out a horrible amount of damage.

Amumu can be built in many ways but items such as sunfire cape and Abyssal Scepter will help maximise damage output and a well timed Randuins Omen can add a 2 sec slow on the end of your ult

When to use Amumu
Amumu is most effective with a team that can make use of his ult so people with high ranged DPS or area attacks such as Miss Fortune, Gangplank, Viegar, Nunu, Kat, Kennen, Fiddle etc are all good team mates as they will maximise the damage output (Hand to Hand DPS are also good if they follow you in and don't waste half of your ult getting into combat)

I always find Amumu to be the weakest of the 3 tanks so its good to have another off tank or tough to take over your tanking duty's as you flash away.

Key Items
Philosopher's Stone
whilst this is my first item i keep it for a very long time to max out the gold gained

Heart Of Gold
also a early item to max gold income I like to finish one of the 2 gold generating items mid game and leave the other till very late game

Abyssal Scepter
Very nice item to max damage output and still gain resist

Notes
Out of the 3 tanks listed I find Amumu ends up being the least tanky.
I also find I can complete my build in about 45 mins so before getting the last item get 5 wards and light up the map this also enables you to constantly have Oracle's Elixir and all 3 stat Elixirs active after 45 mins.
The timing of your ult can and will win or loose the fight so timing is everything.
I find Amumu the least stable of all 3 tanks but the most likely to give your team a ace with no deaths.

Role
your role as Rammus during the lane phase is to feed the hell out of your partner, to do this well you need a high DPS champ who can make most of your taunt.

Remember DPS chars need to be fed you don't. What your aiming for is a even or slightly positive kill to death ratio with a load of assists. This should take you into team fights with the ability to Tank it up whilst your fed team mate unloads hopefully putting the fight in your favour.

When to use Rammus
Rammus should be used when you have a high DPS char such as Kat as your partner and your team needs a full tank to take the pain.

Key Items
Philosopher's Stone
whilst this is my first item i keep it for a very long time to max out the gold gained this is normally my last or seconds to last item to finish

Notes
Rammus is my favourite tank his ability to hold off an entire team at a turret can be a game changer. His damage output can be rather low until level 6 but taunt and powerball is hugely effective at setting up a kill.
Early game your job is to feed your DPS so max taunt early. During team fights try disable there main damage dealer I do love taunting Master Yi to watch him destroy himself on my thornmail and defensive ball.
Rammus is the defender of turrets I am most happy sitting at a turret with taunt ready facing 2-3 opponents, just tag the squishiest and watch him die.

Role
your role is to protect people with your ult and if possible punish there attacker for being stupid enough to over extend with your ult off cooldown.

The general tactic is ult in, taunt through them, and attack

During the lane phase this is easy to pick who to protect but team fights you have to be careful who you pick. There is no point picking annie if she had already done her nuke as her damage output is relatively low, Always consider who has the most punch left in the fight and keep them kicking (keeping Yi alive so he can life steal his health back up is usually a good choice).

When to use Shen
Shen requires a lot of map awareness and communication between the team and you also need a partner who wont instantly die when you ult across the map, if you do not have this then do not pick shen.

Shen also requires some attack ability to properly punish people for trying to kill your team mates so ensure your team can survive without a full tank. Teams with high CC do very well with shen

Key Items
Frozen Mallet
As you will be taunting through people and hopefully killing them this item will ensure they don't escape.

Last Whisper/Hexdrinker/Bilgewater Cutlass
I choose one of these items depending if the team is heavy armour/heavy magic/any other situation. These are all good little damage dealers that are quite cheep with useful ability's.

Notes
Shens taunt is the weakest taunt/stun out of the 3 tanks but it does have mobility uses, fully done you have a 2 sec taunt and if your taunting through some one you will only have about 1 -2 hits on them before there free to move again as they will have to walk to you so I always love to back this up with frozen mallet which give you the ability to setup kills early game.
Vorpal Blade is very handy for health regen remember to share this with your lane partner to keep you both at full health as this will give them the best chance of survival when you suddenly ult across the map.

Im going to describe how to create a full tank some situations will require you to make a off tank but for the 4 or so items that will make up the Tank part still follow the following

1) never overdo a attribute
you need to distribute your stats having about 150 more armour than people have armour reduction is about the optimal amount of reduction for you money and same goes with magic resist. You need to get a fair amount of armour/magic resist and back it up with a fair chunk of health but overdoing any can leave you weak.

Regen is important as this will make stand off's benefit you but to much regen is a waste, I have also seen sion etc build as a lifesteal/regen tank which is fun to play but hugely unstable some times you will run through a team others times you will die within seconds, this kind of instability is just what you team really DOES NOT need from the tank. Additionally regen is easily countered with Ignite or Executioner's Calling.

2) don't leave a weakness
you need to be aware of what the other team is purchasing and be aware of who is doing well. I normally purchase a regen/health item and boots near the start as this will give people time to purchase other items and get settled in giving you the information you need.
ideally you want the other team to be heavily stacked either magic or physical as then you can overdo the armour/resist and back it up with more health but this is rarely the case.
being aware of who is fed can be a game breaker if your against 4 physical and 1 really fed magic dealer it may still be worth building your armour/resist evenly, tanking is all about realising where your damage will be coming from and countering it.

Tank Items i like
General Tank Items

Anti Magic

Anti Physical

Other


Aegis of the Legion - good all round items more so if you have people who will be near you in the fight, I do find this item underused as it doesn't have a obvious dramatic effect like others.
Banshee's Veil - health resist and blocks negative spell this item is essential in CC teams.
Force of Nature - loads of resist and regen and a handy speed boost which will complement frozen mallet.
Frozen Heart - I tend to under use this as I find the mana often to be a waste but if you are having mana issues this is a brilliant item.
Frozen Mallet - lots of health and a slow that should never be underestimated.
Guardian Angel - can be a handy item i normally only get it late game when I need to top up both armour and resist.
Quicksilver Sash - high CC team and you didn't take cleanse? then get this massively underrated item.
Randuin's Omen - expensive item but one that can easily fit as a core item in a build just remember to use the damn active ability on it.
Sunfire Cape - a good item to back up thornmail with.
Thornmail - the best counter for any DPS get it early and back it up with some health.
Warmog's Armor - huge health boost I tend to get this item early if I know I will be lacking in other health giving items.
Zhonya's Hourglass - I only really get this if facing Karthus but its also a handy way to add more punch and armour.
Shurelya's Reverie - my favourite regen item for tanks which I tend not to complete/sell till late game to make the most out of the gold.

Boots
Mercury's Treads - 90% of the time i go with these for the resist and CC counter.
Ninja Tabi - for the few times you don't need Mercury's this is normally the alternative (remember to consider slows and stuns before purchasing theses and if you will be getting quicksilver sash or if you have cleanse).

Other items
There are many other items that are viable especially to an offtank personally i like Bilgewater Cutlass on shen (flash + taunt + custlass gets a slow from a very long distance) or Atma's Impaler if you start to get a lot of health and Abyssal Scepter to add more punch to your spells.

During a team fight you job is to take as much damage as possible that would otherwise be directed at a weaker team mate and then survive.

Any good player knows the tank will take the longest to kill and so there right at the bottom on the kill list at the start of a fight but to effectively do your job you need to be the prime target so how do you raise your self up the kill list

1) be all in there face. if you are the nearest target then many people will target you as they perceive you as the biggest threat to there weaker characters

2) carry an Oracle's Elixir as this will mess up any stealth chars making you a prime target to get them back in the game, this also enables you to target them with taunts etc and get a quick kill.

3) kicking out some damage is a good way to raise your threat level a good item for this is sunfire cape for Rammus and Amumu as it can be used with there area ability's and stil help to protect you.

Other Tips
Be in every team fight. Shen has his ult Rammus has power ball and ghost if needed and on Amumu i take teleport to ensure you are in the fight.

do not waste your taunts/stuns most teams have 2-3 prime targets you want out of the fight quick targeting some one else or even worse there tank will most likely loose you the team fight

Remember your strong points and play to there full potential

Take your time and get your ability's off perfectly I've had random teams screaming at me on a off tank Amumu to initiate which was complete suicide waiting 20 secs longer gave me the perfect timing as I managed to lure out there characters going for a side swipe and ult the entire team.

Remember your not invincible, true you can take a hell of a pounding but you can and will go down if you put yourself in bad situations.

Protect your damage dealers without them you will drop even a full tank Rammus has a very limited life span 1 v 5

If your new to tanking I would say Rammus is the most strait forward tank to play so it probably best to start there, he is the most forgiving of the 3 and requires the least team coordination and so is very good for random teams.