RoA + IBG +20% CDR Runes/Masteries AP Tank Sion seems a lot better top than AD Tank Sion
You just max E for insane wave pushing on a low CD and then W second for an insane amount of shield and AoE health damage. Your lane and late game seem at least 3x better than AD Tank Sion's lane or late game.
From the games I played it didnt even matter that I had no AD for my Q since its a high ass total AD ratio and its mostly useful for the Stun if you happen to land it, which is rare anyway. Might as well get off the shield + E damage in fights.
You rush RoA and IBG then just build full tank like you normally would, getting either Visage/Locket or even something like the new Ohmwrecker