THD is strange hero, hes neither true supp nor ganker his abilities are much rather pushing AoE dmg, so items should helped to this role, a bit of support and AoE presence - mana boots fo you to spam fire and for team to stay for push longer, meka for team heal to push and fight longer, if great job done you can afford shiva or hex, imo shiva for him better over hex cause hex is build by another hero for sure and your armor sux, also its cheaper
, agha is waste imo, even numbers looks nice, but if you got harder time, buy point booster before shiva to get more HP/MP so youre more tanky, in later game you could finish agha after shiva if wanted, still alone booster is fine and hex should be higher priority... magic wand is not mentioned its must for all heroes and if you got really tough times at starts go for PT to have extra HP/MP but with fire you can hit creeps and heroes so imo not big deal to rush mana boots
but there can be also alternative build if team needs - jango gives stats dmg and MS/AS and youre AoE pusher/supp, also new rod can be good - gives int and HP and cripple ability so youre good even after casting all your spells