Well this is my second build for 3's.

Help your jungle on the wolves and the wraiths with your q, he always love some early help.

You can switch for charm LvL-2 if u want full cc kill on lvl 2.

When you get your ult, don't suicide on it and check your ally as you can easily drop all you have on the enemy without endangering yourself in the process.

I buy the Blackfire and the Morello for the CDR+SPELL PEN and the amazing proc.5% damage.
You can use every spell to do damage so try to distribute to your enemy some juicy sauce.

You can always switch the 3 other items, starting with the Rylai's if u need some slow or if you want SPELLVAMP get the Hexteck or the will, as you may not really need the aura on the will if ur the only 1 to caster on your team.

The wooglet Gives you a good save if you get focused during your ult, never forget about it.
You got a 49 sec CD on your ult and wooglet is 90 sec, so get that ult working as much as possible

Pick the boots as u like it, i don't put mine but i always uses sorc boots. I would take Boots of mobility someday to troll a bit, as the speedboost can be funny with wooglet speedboost.

If you dont feel like it, you can skip the second doran or buy 3, it's not a perfect science.