The highest priority for stats is cooldown reduction to get to the threshhold of perma slowing with ur E->W, also cooldown on ultimate is worth way more than a full item would give you.

So spending 800 gold on the cdr is way more efficient since you usually don't care too much about stats like AP/actives/heal increase which are really expensive.

Example for this is redemption is 2300 for 15 Haste, thats almost 3 Kindlegems which give you 30 haste already.

Obviously this is my own preference and you can adjust the build as you feel comfortable, forcing a itembuild you don't feel or like wont help you too much either; I just think its the most optimal.

Main reason is that you dont spam abilities early on either way, mid-lategame your slow usually means a kill so presence of mind is more than enough to keep you full of mana. Archangels is also extremly expensive compared to just spam-buying cdr.

Only time I would ever go tear is if you're on a smurf and overstaying a lot of times or just being on the map way longer than u usually would be