I am going to introduce to you a very solid galio build viable for ranked, I've been experimenting alot but this is the build i find best. With this build you wont at all be that tanky, but you will deal tons of damage, the reason why you shouldnt build full tank is because that will leave your team at disadvantage since the other team will have an ap carry that deals alot of damage and you will just stand there looking dumb after your ulti. With this build you will fill that AP carry role pretty well and deal alot more damage than you think. Your main job is to get off a perfect ulti so why not make it hurt like hell? You will still be a bit tanky but not entirely unkillable as you'd be if you followed other guides.

The main reason why I am using these runes are to make use of his passive as much as possible. If you start with the +20 Magic res item ( that later will be built into Chalice ) you will have about 90 magic resistance at level 1 and about 45 AP, that is ALOT. The magic pen reds are standard for any ap carry and they will make you penetrate hard early. The armor seals are simply to make you tankier vs ad junglers and basic attacks from the mid champ, simply because you are melee and will take some auto hits when trying to last hit i find these very useful.

The skill sequence in this build is focused on damage and easier farming, however if you are having big trouble consider maxing "W" before "E". In any way try to always max Q first as it is your main harrassing and damaging spell.

Also it displays that you will have 280 AP with this build but i assure you it will be alot higher, they dont count his passive when they calculate.

Chalice Of Harmony - A must have since it gives all you can wish for as galio, it will make your mana almost infinite, it will make you tanky to ap and it will also give him damage because of his passive. Really good item, however you should sell it when you can afford aegis as last item late game.

Mercury Threads - Makes you less vulnerable to cc and it will make you even tankier to AP, + some ap to yourself again thanks to your passive.

Abyssal Scepter - A must have on all galio's, it gives you tankyness and about 100 AP + a nice aura to weaken your enemies.

Deathcap - Simply for the damage.

Void Staff - Same reason as deathcap, also makes you able to do damage to the tanky enemies.

Banshee's Veil - Great deal of tankyness and AP again thanks to passive and also it makes it harder for your enemies to interrupt your ultimate in teamfight because they first have to get through the shield.

Aegis - Nice aura to team and makes you generally tankier.

You should always have flash on galio, no matter what, no excuses... simply because of the fact that his ulti can be extremely game changing and flash+ult combo can surprise the enemy. I use heal simply because it will make you even harder to kill and you can just farm forever and win cs by alot. You're not in mid to kill you are in mid to just laugh at your enemy and win farm and win late game.

The reason behind these masteries is that i want to remain tanky while grabbing the main damage spells in offensive too. you will get alot of cooldown reduction from this mastery setup too so it fits Galio good since his ulti has a rather long cooldown.

Before the teamfight try poke as much as possible and when the fight starts try find a way to land a perfect ulti, by perfect i mean landing it on ~3 people, preferably the ad carry involved. Never hesitate to flash ult if you see an golden oppurtunity. Use your "W" on whoever being focused in your team.

+ Strong Laning
+ Good damage
+ Best ultimate in the game
+ Decent support spells
+ Hard to get ganked
+ Easy farming
+ Good poke

- The only bad thing is if your team start a teamfight when your ulti aint ready, that can be devastating.