first you start out with trinket of restoration
+ the small shield .. chance of 20 dmg reduction…

then you get life tube.. and then the last item for black helm

THEN you get another lifetube.. and after that one.. mana tube..
and then you get the 10str-10dex-10int item.. and then u save up 850 and buy nullstone

by now you got loads of HP regen..
loads of mana regen..
most of your dmg comes from spineburst. wich you can walk around and spam almost to keep up 3 things for your ulti ( im tired and cant remember the correct names
after nullstone you get STEAMboots.. with str ofc..

by now you are pretty damn impossible to kill 1vs1
depending on your mood you can go for behemoths heart or mock

i prefer mock first and then behemo..
but most games only last for 1 of those last items..

i just had a 1 hour and 20 min long game with armadon. having 4200 hp and 48hp/sec

arma is good for tanking lategame.. ofc.. and ultra lategame he does little dmg.. compared to the opponents hp.. thats why you wanna get mock ..
so with spines + mock you do 62.666 aoe dps alone
and hitting for like 300..

imo armadon is crazy good mid/late game to take down Int heroes….
oh well.. give my advices a try and you will see that armadon can be played even better with those items.. hp regen until midgame is key to survive and win