First thank you for commenting. It has so many views but no comments.

Second, yes his AP ratios are good but his kit is a tanks kit.

"Tanks. What are tanks? Is a tank just a champion that's really hard to kill, or is there more to it than that? I'm about to explain to you what I believe is the main criteria for being a tank.

First off: Initiation. Every true tank in the game has some form of initiation, most of the time it's a gap closer, although in some special cases it is not.

Second: Heavy disables. Almost every true tank has at least 2 forms of heavy disables in the form of snares/stuns.

Third: They effect entire teams. In almost every case a true tank has abilities that will hurt the entire enemy team, if they are bunched up close enough, all at once, giving your team a distinct advantage during this period.

Fourth: Shields. Almost every true tank has a shield of some sort, although so do many DPS champions, support champions, and off tanks. The difference is built around the rest of the champions kit

Typically every true tank in this game has all of these traits, and their kits are built around light sustained damage of some form, and getting in the way of the enemy. Using various forms of CC to control the enemy, as well as shields to absorb damage, and an initiation move to get into the action at the right type, they are not build for burst damage, they are built for taking damage."

From: http://www.mobafire.com/league-of-legends/build/a-manual-for-tanks-129679

[Just a note: I really like this guide and feel that it is important to look at. Although I have Volibear as a tank rather than offtank (even though he is definitely an offtank with his execution attack and focus on killing rather than stopping the other team) it is still a good guide to look at for anyone who considers using a tank.]

1) Initiation/gap closer - Q
2) CC - Passive, R, not quite E since it is a slow so it isnt a form of hard CC
3) Affect entire team - E, R
4) Shield - W

He fits EVERY single criteria to be a tank. He has good sustained damage without any AP and can have his shield up at all times which is based on 10% of his bonus health. Thats A LOT of Health. He is basically a perfect tank character and the CDR gets you to have your shield up at all times which is really nice. If you want you could get the CDR mastery in the defense tree then you can switch out the shurelya's with a spirit visage to get more Magic Resist, but I think that it is easiest with shurelya's plus it give the nice speed boost.

Every team needs a good tank, but if you dont fully tank with Nautilus, you end up hurting your team IMO since you cant take any damage without being completely destroyed. Look at team comps, AP carry, AD carry, Tank, Support, Offtank/Tanky DPS/Melee Carry. Its rare to find a team in need of an offtank/tanky dps/melee carry since everyone seems to want to play riven or wukong or garen or master yi, but usually the teams struggle with tanks. Your thought is to make him an offtank but he is designed with a tank kit. Why do YOU have to do damage?. Why cant your AD or AP do damage? Thats right, they died because you focused on damage instead of tanking and now its your job to kill the enemy with your much weaker attacks. Yes AP is COMPLETELY POSSIBLE, but NOT OPTIMAL. People are going to assume that you are the tank and will be expected to tank, but a RoA and Rylais do not make you a tanky enough and you'll end up causing your team to suffer.

I was a tank in a fight where my team was trying escape and lasted long enough to interupt the enemies attack, prevent them from killing my AD, then my AP and support while I constantly retreat ping so they go back to base and survived long enough for my AD carry to come back and clean up the weakest enemies allowing us to have a 0 for 3 exchange. Thus the IMPORTANCE of a tank. If you dont have any resistance like armor or magic resist, then you will die and with you dead your team will have to be passive. If I had built something like what you are describing, I would have died when they focused me and they would have destroyed our turret. Possibly getting my other teammates, but not likely since they took a while to focus me and I interupted them enough.

I almost never build around Nautilus health because he NEEDS ap to do any damage, war mongs is just not needed. He isn't a tank hes a fighter. you need items like RoA and Rylies building AP and health then rabadons, lichbane but by the time i get into anything extra game is usually won