This build will do Cho gath to be a Tank.
Read texts below to know about it.

It is better to use this because you can reach any tower to defend it in some seconds.
you need this also to catch your opponents when they are running back.

This boots make you really faster.
you need this to get your oponents when they are running back.
you will have about 405 speed movement.
This boots will give you 3 enchanced movement.(1000 gold total).

This armor is perfect for a lot of health giving you 920 health and 30 health regen per 5 sec.Champion kills and assists grant 45 health and 1.5 health Regen per 5 sec. Bonuses cap at +450 health, and +15 health Regen per 5. This armor is good for surviving and tanking. you can buy guardian angel first instead of this but its not much good as recomended.(3000 gold total)

This armor is also good at surviving cause it gives you a bonus of 750 health and 375 mana when your champion is killed, reviving him so you can run away from death.This effect can only occur once every 5 minutes. It also gives you 68 amror and 38 magic resistance. You can buy it after buying the boots but it works better when you buy it after warmog's armor. (2600 gold total)

This item is good at cooldown reduction cause it reduces all your colldowns by 20% and also reduces attack speed from all nearby enemies by 20% (1000 range). This item gives you 99 armor and 500 mana. It is good for attacking with many spells repetidly so, if the enemy is faster you can use ghost or use Q again and again. (2775 gold total).

For last buying you can buy warmog's armor again but it is also recommendated to buy some life steal like the bloodthirster.(Gain an additional 1 Physical Damage and 0.25% Life Steal per kill. Maximum of +40 Damage and +10% Lifesteal. Bonuses are lost upon death.) Also gives you 60 attack damage and 15% lifesteal. Good Luck.

it is recomended to use the ulti against minions or easy killing monster cause then you will grow up and have much more health.( remember that ulti does 1000 damage to minions or monsters!!)

Ryze is having a lot of AP and Mana for his spells, so he can cast many spells repetidly thanks to his passive (all spells have -1 sec cooldown when you cast a spell)
Read below to know about this build.

Ryze is a champion that have low health so, he needs ghost and flash to run from death. He also need these spells for catching the enemies and kill them.
It is recommended to use the Rune Prision spell to snare their enemies after casting ghots or flash.

This item is really good for mana and mana regen.
it gives you 350 mana, 7 mana regenerate per 5 seconds and each time your Champion uses an Ability their Maximum Mana will increase by 4 Mana. This effect can't occur more than twice every 6 seconds. Bonus caps at 1000 mana.
This will help you to cast spells repeteadly.( 995 total gold)

This item is good for magic and movement. It gives you 20% magic penetration, what is really good for Ryze cause of his magic spells and gives you 2 enchanced movement that is good for movement and catching your enemies. (recommend to use Rune Prision spell to snare enemies when getting at them).(1100 total gold).

This Item is Really good for Ryze cause it gives you some health, mana and Ap.
It gives you 450 Health, 525 mana and 60 AP.Your Champion gains 18 Health, 20 Mana, and 2 Ability Power every 1 min. Bonuses cap at +180 Health, +200 Mana, and +20 Ability Power.
(3035 total gold).

This item is good at cooldown reduction cause it reduces all your colldowns by 20% and also reduces attack speed from all nearby enemies by 20% (1000 range). This item gives you 99 armor and 500 mana, so it is really good for Ryze cause he can cast many spells with low cooldown repeatidly.(2775 total gold).

This item is the best for AP, giving you 155 AP and 30% AP.
When Ryze have so much AP, his spells will be much stronger than before... =).(3600 total gold).

This item would probably get your mana and AP really higher, so your Ryze will do much more damage with his spells and will be able to cast them more reapeatedly.
This item gives you 400 mana, 25 mana regen per 5 seconds and 45 AP. Also, 3% of your max mana is converted into AP.Each time your Champion uses an ability their maximum Mana will increase by 4 (capped at 1000). This effect has a 3 second cooldown. (2855 total gold)

You should probabbly buy another rabadon's deathcap so your AP get much higher.
well... thats all. Good Luck and plz vote for +.... =)