Ok, this build is good. But slow to start out with, so you might want to farm. But sometimes I dont farm and do just fine.
Anyway, I start by getting his first build item... of course. Then I snag tear of goddess without building for it, you can alos get sorcerers boots instead of the tear of goddess. But then I might grab Amplifying Tome, if not I wait until I have enough for the Archangels staff, which adds a lot of deaths to my score... but if you want to counteract this inevitability you can build for SHEEN, its a blue sword thing in Ability Power.

Now your probably at the place in the game where you have A LOT of assists with my build, this is because I dont build for AP much, I just like to snag mana and near the end I may consider building AP, but if your team will cooperate. You can support them instead of farming or tanking yourself to death... BTW Ryze isn't support, so all you really have to do is stick by a good friendly champion and RUNE PRISON everyone who try's to attack your buddy, and then go APESH*T with spells on them.

Just to start off, if your in a lane with LUX on the other team or Ashe... swap lanes with someone who is a range so you can fight up close, because LUX will ride you the whole game if not.

Sejuani like most champions, are Over Powered... SO USE THEM!
I start by getting her Shield, then Ill get Kindlegem.

Sejuani starts off pretty good, but you have to avoid taking a lot of dmg at the first wave of minions so you can boost your level to 3, while the enemies or your teammate in the same lane is almost level 2 or even level 1.

Sejuani is a great solo, but if you have a good team that will help you, then you will be pissing people off left and right. Sejuani is a master of Slowing-Constant DMG. At a higher level lets say 6, you've gotten your ULT by now hopefully, and you see 2 enemies just chill'in.

Hit them with your ULT and they cant move, you might want to do this while your close up as well, So they are both stunned and you go in with your Arctic Assault, this deals a lot of damage, Activate NORTHERN WINDS and chase them until you feel its time to end their lives.

Hit them with PERMAFROST and start all over with ASSAULT and Northern Winds. this will STUN-DMG-SLOW and possibly at the end... KILL

Ryze is a better Farmer then Sejuani, but they can both do it.
Ryze is a range so he can stay in Bushes and things to cover himself, and still farm without really being detected by anything other than minions, unless your trying to kill champs, if so... Good luck:D

Sejuani is another OK Farmer but she is Close-range, so you might need to Assist a friendly turret in killing minions instead of sitting back and getting all the EXP from it's kills.

Sejuani can also Farm without turrets but it is still not as effective...
Sejuani deals A TON of damage, so use it on minions to get a lane moving faster if you have no allies or minions in your lane at that moment, let the minions pile up and think

YAY WE GET A FREE KILL YAY!

then you Arctic Assault and Northern Winds, And lastly PERMAFROST for the kill!

Its pretty much the same as killing a normal champion, but you can kill a whole land in 3 seconds.

Cons - Sejuani isn't very good when it come to fighting Range Champions, you want to be matched up with Close ranged champions on the opposing side. So if you get Ashe and Lux, or Sona in your lane. You better switch lanes with people.

Pros - Sejuani is an Excellent Support Tank, with the ability to gain kills, and if you dont want to, you can gain Assists like crazy. She slows and traps champions and then hammers them with constant damage then dealing instant damage at short or long rage. Her ability to carry so many and still assist like a boss is what I consider the perfect Champion to play for beginners and higher.

Cons - Ryze if good for keeping close range champs at a distance while still hurting them. But he has a weakness... Warwick is a wonderful HAND-2-HAND champ, you can try to trap him and attack, but This build doesn't really hurt Warwick enough to stop him from killing you if you are blood scented and Hunger Stricken. Also is slow at leveling but good in the later game.

Pros - He can Trap targets and let teammates go to work on their face, getting you an assist.
He is also a good Farmer. He has a medium range but can keep most close range at a distance and trap them if they try and run.