I just recently purchased Malphite and am learning how to play him. I almost never play solo; I'm usually on Vent with at least one other player, most of the time two or three, sometimes a full team.

I bought Malphite for a few reasons: He is an amazing Jungler from level 1; he has great survivability, which makes him much less likely to get ganked in many scenarios; he is a great ambusher.

Since his armor nerf, I've been taking the Defensive tree (I'm only level 14, so no 9/21/x for me or what have you) to make up for his early game. I've been following the old Jungling guide:

1x Cloth Armor
5x Healing Potion

Summoner skills: Heal, Smite. I seem to need Smite to make up the damage at low levels to kill the Golem and the Lizard, and I seem to need Heal to survive, even with the health potions. I tend to hit the Golem first and work my way around to the Lizard last, then go buy, then hit the other jungle.

First, I buy Heart of Gold as per the Jungling guide, then start working on Warmogg's Armor. But I'm not sure how much this helps. Should I, as Malphite, be stacking health (great synergy with his passive)? This produces a tank, yes- but Malphite seems to not be terribly resilient in the late game, even with 4k health. It goes without saying that most champions die when focused but they tear Malphite a new one, for him being an "in the thick of it" character.

By the end of the game, I tend to have worked on. if not finished:

Heart of Gold
Warmogg's Armor
Mercury Treads (level 3 boots if enemy team doesn't have a lot of CC)
Frozen Heart

I'm not really sure where to go after here. Stacking health seems to be great for survival but not for damage output. Even stacking armor is too expensive to give appreciable results. Cooldown reduction is great but it makes me totally reliant on the Golem buff, which can be very competitive to get later in the game. Is the Chalice worth getting on Malphite?

Any suggestions would be greatly appreciated, including gameplay suggestions (for example, my ultimate is great for Initiating but Malphite doesn't seem to have enough "put down power." I'd take Ignite or Exhaust but I just can't afford to lose Smite and Heal right now.)

rally is better than heal for jungling.
i like saph crystal + 2 health pots.
i like catalyst on malphite.

Do you upgrade Catalyst at all?

And how badly does the lack of armor hurt you?

A common build I used to use was:

Catalyst
Mercury Treads
Aegis
Frozen Heart
Banshee Veil
Guardian Angel

However, since the addition of leviathan and the nerf to catalyst and aegis, im trying new things

Any other opinions? I've been somewhat underwhelmed by Malphite. My ability to kill people seems really limited, it seems like they get away far too easily, and my damage seems pretty weak. Even my survivability is questionable as a tank. Amumu seems like he does more damage and lasts longer as well.

Sunfire capes - stack them. The armor helps his third skill great. Farm like a beast, and don't die.

I normally get mercury treads. If they have a bunch of magic damage, start getting magic resist items, normally banshee's veil for me because you can build it from catalyst.

You're not really supposed to be a killer with Malphite. He's a tank and an initiator... Sure, you get some games where you'll get 10 kills, but for the most part that won't happen. You'll get a ton of assists though.

I build him differently depending on the team I'm facing... A "normal" setup for me would look something like this:

Catalyst*
Mercury Treads
Aegis
Frozen Heart
Sunfire Cape
Spirit Visage/Guardian Angel/Force of Nature

*Catalyst->Banshee's somewhere in the middle

I don't jungle though, I lane. So that may make a difference, but not much. And armor affects his passive, not HP (from your OP about stacking health with Warmogs)

The way I build Malaphite is:
Ninja Tabi - for more armor/dodge/movement.
Glacial Shroud - for more mana/armor/cd redux for ult. I always feel malaphite is mana starved at the beginning of the game.
2x Sunfire Capes- again more armor for 3rd ability/health

After this your a beast, sitting at 3k life and already beefy against any melee character and hitting for atleast 500 on your spammable aoe attack. Not to mention as soon as you charge and slow they take constant damage from your capes. Might not seem like much (50 - 80 dmg a sec) but your a tank and in their face while spamming your aoe.

If you start having problems with casters then slap on some magic resist after that cause farming is a joke your capes/ aoe eats a wave if you position yourself between the casters and meleers.

But I don't play Malaphite as a jungler. :S

Granite Shield - Malphite is shielded by a layer of rock which absorbs damage up to 10% of his maximum health. If Malphite has not been hit for 10 seconds, this effect recharges.

I've seen it claimed that the passive damage absorb happens after armor/MR damage reduction so in that sense stacking armor or MR should be the same as normally deciding between those and health. Haven't seen anything conclusive on absorb working like that though, Udyr has some too from Turtle Stance.