Prepare for rediculous amounts of health and ability power, whole teams will fall before you

Magic Pen - Clear to see
Ability power - Always nice to have a small boost
CD Reduction - Needed to reduce pool timer and help with q and e spams
Health - Nice to give yourself a little more survivability off the bat.

If your doing great with no fall backs skip the spirit visage for another rylais crystal scepter. If you need magic resist skip a scepter for a banshees vail, make replacements where needed