I've been thinking about assorted builds a lot lately and I've gotten stuck on wondering when to build tear. What conditions should exist before choosing that as your mana item if you're a mage in mid lane?
To clarify, I don't mean which back. I mean which champions and games is it good in?
or 
.
quickly? 
's passive by building other mana items? 
(Are you content to continue farming for a large period of the game? Can you contribute meaningfully without damage items?)Whether you build Tear or not should probably be decided before you start a game; your own champion has the greatest effect on whether you should build it or not. However, if you're a classy old-timey mage that can build and , you could build 
before if you're having trouble with health sustain early on. The same logic applies to (ex: you could build before as 
if you're somehow losing too much health in lane).
tear is very situational and theres a lot to consider before buying it. While on some champs its practically a mandatory buy (thinking AP kog, yorwick, maybe anivia) other champsshoudlnt get it because its too much gold spent on an item that doesn't have combat stats. I only buy it under certain conditions. usually when my jungler isn't giving up the blue buffs and only when my team is far enough ahead so that I can afford the 700- gold sink. The item is certainly strong late game even if you don't upgrade it just because youll never go oom but you have to remember that the enemy mid laner wouldn't be getting away with 20 hp if you went for more ap instead of the tear. Basically, whether the item is a good buy or not is situational to whats going on in the game you are currently in.
Either first or second back for me. Depending on how long I was in lane. If I have enough for tear/boots/wards, I will go for it. If not, I go for a 2nd Dorans ring/boots/wards/pots. But the sooner you build it, the longer you can stay in lane.
on mana scalers or mages that have at level 18 a base mana pool of 1000 or more
and always as soon as possible
In a way there's a few factors to consider in the realm of heavy mana vs heavy mana regen.
The biggest one is the initial lack of AP and CDR that going with an early tear+ROA gets you.
The other really big one is whether you can stack the tear well enough, and whether you have other core items you need to finish before upgrading the tear (Viktor for instance, seems to work pretty nicely with tear seeing as how his hex core gives a decent amount of mana, but he's not able to spam quickly enough after getting tear and needs to sink a good 1000 gold into the first hex core upgrade before he can think of finishing a Rod of Ages, much less archangel's staff). Sometimes stronger core items (like sheen/lich bane) takes presedence or the champion just doesn't spam spells regularily enough for the Archangel's staff to graduate into a full 120+AP item in good time.
And then there's of course how well use you can make of the mana otherwise, and what other items you're building.
If you can get your AA's fully charged into a Seraph's Embrace by the end of the mid-game, then you'll be sitting on a vast quantity of mana, only 50% base less than Morellonomicon, a 120+AP item, decent amounts of health regen if you pick up the utility masteries needed and a cool little bit of utility from that shield.
But if you take too long to get it to AA's in the first place, or if the regen isn't enough (remember to get an 
for all the mana regen you'll ever need), or if you need the CDR and have problems getting it elsewhere, or if the AP/MR you get from the components of Athene's/Morellonomicon could make or break your situation, then the investment might be too long term to be effective.
Lastly, on a game-to-game basis. Both RoA and AA's have very heavy build paths, meaning you usually can only get a new full component at 800 gold or more. Compared to Athene's/Morellonomicon where each component costs no more than 500 and is usually very useful to sit on by itself. It'll be a lot easier to go for tear->AA's/RoA in a game where you're getting good farm and manage to stay in lane a long time without backing, than one where you get zoned off from some CS here and there, or have to back frequently for whatever reason. Simply because you can always manage enough gold for a part of or 's build paths while 
and both require 
which costs 860 gold, which can be surprisingly high at times.
Generally most mages are better with / or / . It's usually a case of you get tear on that champ or you don't, although in some cases it is debatable (
can go any one of the mana items, doesn't matter). You don't want to go two mana items because you will lack way too much damage.
It used to be used more before the buff. For example, as 
vs 
You would go 
, but not you just go Morellos
When you have 720 gold is when you buy Tear.
