Predecessor Builds > Argus > Big Damage

This focuses on mana regen and then raw magical power.

A more aggressive build would be Orb of Growth first leaving out timewarp. This loses most of your magic regen but adds an extra 57 magical power plus a heal on ability cast. I prefer high mana regen for good uptime on RMB and abilities.

For 4th item, choose based on what you need:
Combustion for burst damage against squishy enemies and long team fights
Megacosm for shredding armor-based tanks and more poke based fights
Noxia for burst damage against high health enemies and more poke based fights
Dreambinder to lock down slippery heroes and long team fights