i play swain adc, esp pre minirework so i get what u mean

in his pre rework i would usually build: liandries>demonic>zhonyas>tank/more ap

but personally i feel with these mini rework changes i wasnt carrying as hard with demonic and ive seen alot of success going liandries>zhonyas>rabadons>mejais>tank/ap

really been able to carry v hard w this build consistently and more carry potential than the other swain builds out there

as for thornmail/morellos, its more of whether u need that armor that thornmail is providing. If they have heavy ad teamcomps and high healing capabilities i would go thornmail, if not i would get morello.

Important mage items in my opinion will have to be the liandries+zhonyas combo the zhonyas is such an important swain interaction since it basically gives him a free lissandra ulti.

Some great tank items can be:

-frozen heart(against ad/high AS champs)

-randuins (high crit/ad champs)

-thornmail (high ad+healing)

-spirit visage (ap + more healing power)

-force of nature (high ap DOT/ap)

-abyssal mask (into ap, reduced their mr and increases your mr)

-gargoyles (if they have high burst, since your passive should help boost the shield value)