it depends.. currently i'm using 3 diff builds for diff situations:
1) full dmg build: haas claws, warrior boots, endless battle, bloodlust axe, magic blade, blade of despair
2) full tank build: dominance ice, magic boots, oracle, cursed helmet, courage bulwark, brute force breastplate
3) fusion (half dmg+half tank) build: magic boots, bloodlust axe, endless battle, oracle, bloodthirsty king, immortality (can be switched to other def item depending on situation in later part of game)
i most commonly use #1 - but only if my team has a tank and support. if team no tank & no one wants to tank, i'll use #2. if team has tank but no support or has support but no tank, i'll use #3. really depends on situation & the characters my teammate choose as well. like sometimes i see my team got no tank but got support & high durability character (e.g chou), then i'll still use #1.
but as & when i got time to look thru youtube vids i will also modify my builds. sometimes i see the builds that those streamers use, i'll try them out & if good i will use. then sometimes i'll tweak my own too, like i dont really like to use immortality so most of the time i buy another def item instd.
ruby is a VERY good crowd control char, only thing is dmg is low. but if you buy the right items, you get an insane amt of lifesteal which really helps you to survive thru the game. of cos, you have to have good teammates too.. i like to use ruby most if my team has tig and/ or freya - when all 3 of our ulti come tgt, plus mm/ mage outside shoot, we have a pretty good chance of killing most, if not all, of the enemies.