Nautilus is one tanker (just like amumu) which does not require items to do damage and can help team fights easily with his skills.

JUst one note NEVER use dredge line when you see one enemy on sight. Always use it to catch fleeing foes or to help you flee hitting it on a wall.

THe marks and the quintessence will help you have a nice amount of hp on early game+plus your regrowth pendant no heal is required. The potion is just on extreme cases.
Seals is t ohelp yo uget gold, since your farm is really bad and your partner will probably get last hits more than you, getting kills is not a problem but its easily to get ksed tough.
THe glyphs will help you get an advantage against magic foes wich are annoying early game.

Get drege line just to have it in case you need. Maximize your shield, this will help you farm, tank etc....

Playing tanker is always a pain because you must relay on your team, but nautilus can got some kills even without help.

PROS
-need just guardian angel to start tanking nicely
-tanker builds are ezpensive, but always worth, you can get items fast with your gold per second
-funny to play with


CONS
-Expensive
-hard to play with (just play smart and its ok)