Some words to the items:
I prefere Banshee's Veil and Frozen Heart because it gives your some def and your mana grow up and so the passiv of Archangel's Staff too. At the end Zhonnya'S Hourglass give ur more def and the passiv is very usefull in late game team fights.

I prefere to max 1st and 2nd skill first because 1,5 sec speed isnt usefull in early game. WHen you max your heal and atack skill u deals great dmg and heal ur mates too.

You also can take other AP or TANK runes but i prefere this one's. YOu got some magic penetration and some nice mana reg. to heal your mates