When is it more viable to build Deathcap than Rylai Liandry?
Serious question
Serious question
When their tanks aren't much of a problem and you just want to delete squishies at the speed of sound.
Edit: Also anytime you are playing 
Veig actually gets more from Void than he does from Deathcap Prior to 250 Stacks
Why not both? :D
The question is, in which order?
when the damage becomes more useful then utility or as a last item. generally your build as a mage be something like this a mana sustain and cdr item. boots utility item/items pen item/items deathcap
[{quoted}](name=One Crit Man,realm=EUW,application-id=3ErqAdtq,discussion-id=5FrKMtFs,comment-id=0001,timestamp=2016-05-13T13:09:12.142+0000)
when the damage becomes more useful then utility or as a last item. generally your build as a mage be something like this a mana sustain and cdr item. boots utility item/items pen item/items deathcap
no all mages

do people not understand what the fuck generally means anymore? every-time with out fail, i say generally someones like "LET ME POINT OUT THE EXCEPTIONS!"
nope
but
swain is an exceptional general so hes worth pointing out :D
#YesAllMages
Longer ranged champs who don't really need health should get deathcap, and champs who have extremely high ability ratios should get it. DPS focused champs should get liandries rylias
the general build path for a damage dealing mage is
->
-> DECISION TIME!!! do your enemies have MR?
Yes
just one MR item? build some utility AP items ->
->
->
-> 
lots of MR deliberately trying to stop you in particular? ->
->
->
-> filler item likely
consider putting liandries as a third item before void if you have short cool downs and you can reasonably keep the debuff up. otherwise this item exists only for the pen.
No MR on the enemy team?
feel free to get your 30pen from boots/runes and obliterate
(switch these next two as needed, if you need the movement speed or you're confident all you need is the raw damage)
->
->
-> 
rab cap is still a better rush for burst mages who excel with combos getting extra damage, poke mages are better off with ludens when they only get one hit in when they can.
i still highly rate rylias on a lot of mages because its kiting, thats such a strong tool for mages. its also enough to get an escape, or to slow someone down enough to go after them, and thats huge in my book.
Some of the shorter ranged mages get a lot of benefit from roa instead of morello's, and some higher mana cost champs should go archangels instead
thats champion specific, im just offering in general for people who need to kill something.
someone like kassadin for example, needs the roa for when he goes in so he doesn't just die. and the mana pool to keep casting R. swain, large mana pool, bulk, stays in R the whole time, great.
but unfortunately neither of those are going to be the prime source of damage for their team. they accomplish different tasks for their teams. like chase, deletion, or split pushing/zoning.
Edit:Lol woops, thought this was the other comment
Your range and your mobility determines how squishy you build, so when you ask what items you should build, what champ you are playing will determine that. Plus, liandries is pretty lackluster if you don't have a dot tick to prock it alot
tank mage ftw. with all the other activity this last patch, the buffs to spirit visage and warmog's got pretty much ignored. those along with protobelt and roa make for a beefy character. 5th item could be abyssal scepter or zhonya's depending on enemy team comp. i developed the build over many aram games but it's strong in SR, too.
If you are ahead...and the enemy builds no MR you can take Dcap as second or 3rd item.
If they have multiple assassins then the extra health is required from Rylais
Depends... If you can apply the Rylais slow and LIandries burn to more targets and have more up time (DoTs) that makes it better While Deathcap is likely stronger if you rely on burst or have high AP Ratios (Though Voidstaff might be more efficient if the target has 1 MR item)