I used to main Ryze pre-30, so i was pretty bummed when Rito nerfed him. I decided to make a guide so that people could see that he is still playable, and can even carry well since a lot of people i've talked to seem to think otherwise.

AP is always fun
Scaling mana gets more and more mana towards late game, so late game is beautiful
This build really requires that Magic Resist so I found the best way to give him it
Scaling CDR finishes Ryze with the max CDR at 18

Ryze has a good use of Utility side, so i decided to focus on this aspect. Another good thing to put might be defense for the lack of MR, and some attack, along with the Utility. It's really preference, so if you disagree, do you.

Ryze's abilities increase their damage based on maximum mana. This build sets out to exploit this by getting as much mana as reasonably possible. The Archangel's also has this effect by giving a large amount of AP based on mana. All of the items chosen have some sort of necessary Tanky/AP stats, along with heavy doses of mana to improve his damage output.

Q is always maxed firs, because it gives 10 CDR at ful upgrade. second would be E because it also does considerable damage. Last would be the W because it's just a root, it doesn't do a whole lot of damage. ALWAYS upgrade ult when you can.

Ghost- I usually take ghost because it locks down kills early game, which Ryze desperately needs against some champs.
Flash= An alternative to ghost, Flash is an all around necessity for most champions so if you would prefer Flash over Ghost, go for it.
Teleport- A must have for top laners so they can split push well, and be in team fights within a matter of seconds.

A general rule of thumb when laying Ryze is that he has a very good wombo combo. WQEQ or RWQEQ. The more you spam abilities, the quicker his ult, and his other abilities are up. considering that at full build, you will have close to 5000 mana, you can literally just mash buttons and get kills without trying. One strong tip would be to try to get as much CS and kills as possible early game because he has a bad early game, but a worse mid game. Very strong late game though totally worth. Get ROA early so that you can have full stacks earlier. Once you get Archangel's, just spam abilities on minions and enemies so that you can get Seraphs quicker. Avoid assuming supreme tankiness and running into fights alone, Ryze works well as a team.
Use his ult liberally, it is up very quickly, and it gets good health back.
Be wary of enemies with good gap closers like Fiora and Jax. They can easily catch a farming Ryze off guard in the top lane and kill them because Ryze has no real good disengage except for his root, and he is relatively slow early on.

At the end of season 4 ( and any other season for that matter) Ryze was very powerful. He made a couple appearances at worlds in 2014. Now that Ryze has been nerfed pretty badly, there have been less people playing him, but he definitely does have potential to carry teams. Although he is not the best top laner for the current Meta, he is a good alternative to the classic AD tanks that are usual top laners. I personally main support in ranked, but if i were to play top, Ryze would probably be my first choice.

Pros
has a really strong late game
has extremely good burst and CC potential
works really well against mostly AD teams
pretty tanky while at the same time having over 400 AP

Cons
really bad early game (product of Q nerf)
mana hungry earky on (just buy mana pots)
gets shut down in team fights against heavy magic damage teams
people will sometimes mock you because you have close to 5000 mana

Use Ryze as a front line CC killer so that hee can tank most of the damage, but also do enough to get lots of kills. Use his w to secure kills on the focused champs. Ryze is safe to tank most of the damage if the enemy team is AD based, but if the enemy is mostly AP, Ryze shoudl generally stay to the back and get good poke.

Generally, early game farming for Ryze is pretty normal. This changes once an archangel's is bought. when this has been bought, Ryze has enough mana to go ham with abilities and get as much CS as possible, and using as many abilities as possible to get a quick transition in the Seraph's Embrace. everywhere after this point, Ryze is a very good split pusher because he has really high CDR, and can use abilities without mana problems.