I have not played around enough with AP to speak to that yet but as for tank? Here is what I see as best at the moment. Almost 2.3 million mastery on amumu (hardstuck gold yay), anyway here is the build.

• Core: Sunfire Aegis > Demonic Embrace > Boots (plated steelcaps or mercs)
• Pick one then build the other (Thornmail and Abyssal Mask)

Last item:

• If you are against an even team where no one in particular is fed? go with Gargoyle Stoneplate Last item (see below)
• If you are against mostly magic team or their magic damage is popping off? Go with Spirit Visage or Force of Nature
• If you are against most AD team or their ADC is popping off? Probably Randuin's Omen or Frozen Heart

Notes:

Spirit Visage vs Force of Nature: If you have a healer on your team then Spirit Visage hands down. Otherwise Force of Nature gives you more MR after its stacked (80MR total vs 40MR on Spirit Visage).

Randuin's Omen vs Frozen Heart: If they have AA champs with crit items then Randuin's Omen. Otherwise, if they have AA champs building other stuff then Frozen Heart.

Core build: Currently you can solo baron at level 6 (this wouldn't happen in a real game of course) with this core. You can definitely take baron solo when it spawns close to 20 min if you are farming properly. I am usually around level 12 or 13 by this time. Your results may vary. Just make sure your team is shoving a lane with herald or something so their team is there not coming to kill you at baron. XD

Conqeror Runes:

• Precision / Conqueror
• Triumph
• Legend: Alacrity

• Coup de Grace / Last Stand (see notes)

• Domination

• Sudden Impact

• Ravenous Hunter

• 8 Ability Haste / 9 Adaptive Force / 6 armor

Conqueror Rune Notes:

Coup de Grace vs Last Stand. I usually go Coup de Grace but either one of these is good. If you think you will be dueling at low health a lot then Last Stand is going to have more value. So it's a judgment call. You should be learning your matchups. You know if you go toe to toe with a xin you are gonna be knocked up in the air and be 30-50% health super fast so maybe Last Stand vs xin. Debate this in comments and let's figure it out haha.

Aftershock Runes:

• Resolve / Aftershock
• Font of Life
• Bone Plating / Conditioning (see notes)
• Overgrowth/Revitalize/Unflinching (see notes)
• 9 Adaptive / 8 Magic Resist / 6 Armor

Aftershock Rune Notes:

Bone plating vs Conditioning. Conditioning if they have AA jg that you suspect is going to invade will save your life easy. Bone Plating if you think you are just going to be farming for a while.

Overgrowth vs Revitalize vs Unflinching. Overgrowth is your default go to. Revitalize is good if you have healers on your team. Conditioning is good if they have a lot of CC. Look at their team in lobby and make an assessment.