Also carries will buy magic/armor penetration to counter your armor (and Void Staff/Last Whisper are about 1k cheaper than Liandrys/New Bjork) so yeah, health is the easy way. It also makes you stronger against both damage types, so it's never a bad idea to buy a giant belt.
Still, if you're tanking you should also buy armor/mr to make your health more efficient.
Still, if you're tanking you should also buy armor/mr to make your health more efficient.