Don't know if it has been suggested before, but when you buy items with random mana items attached to them maybe instead of having to buy the mana item you could buy a health item instead, so instead of +100AP +500mana +25%AP, it could be +100AP +300HP +25%AP, because I notice at the end of games I normally have 3000+ mana and I can never use all of it, and you can always do with more health. What do you guys think?

Health for spellcasters = Rod of Ages and Rylai's Scepter. Soul Shroud is a caster-friendly item, as well.

If you feel you're too squishy, buy those. If you have "too much mana", you're doing it wrong. You can't ever have too much mana because you can always spam your abilities that much longer.

To build with a health+AP theme, get one or two Rods of Ages and a Tear. Later upgrade to Archangel's and consider filling up with Rylai's and Zonya's. Or mix a Warmog's into your usual AP or Archangel's build.

Also come here to post Rod of Ages/Rylai's.

Also remember that +health is not the only thing that provides survivability. Armor/MR also provide survivability and have a couple items that can be attractive to casters (Mercury's Treads, Chalace, Frozen Heart)