I think Juggernaut is, one of the most fun characters. He is not the easiest, but forgiving. I think he's good to get movement speed up, and roam. He is good at keeping the enemy, behind enemy lines! Good Luck, Have Fun!
To end it, try ether building a Aganim's Scepter, or Butterfly. Both are great, Scepter grants Ultimate upgrade and AGI. Butterfly grants a great deal of damage, mainly because Jug is a Agility Hero. I like the Scepter better because, I like to waist my ULT in a large group. It's just fun! Now just focus a enemy, and unleash Juggernauts Fury!
Juggernaut is a Agility Hero! I like to believe, use of a Butterfly is not needed. So I found a cheaper item, that offers great benefit to him. Try building a Diffusal Blade, it offers high AGI. Plus you'll gain a disable ability, used for ending the chase. Every attack burns mana, also you can slow your enemy. Great job, at this point your not feeding and you farming well enough.
At this point, ether you'll find good use in, Lifesteal or lots of attack speed. I like to use both, first I get Quarterstaff, then Morbid Mask. I like Quarterstaff, because the attack speed stacks with Power Threads. After that your Lifesteal, is worth it.
After you got your boots, you'll farm for your Ultimate. Once you have your ULT, stick with a friend. I found in lots of cases, Jugs ULT may not be enough alone. Of course if you have CRITS, and mana enough for a healing ward or blade fury and your ULT, then you'll most likely be good. Assuming your not fight fed opponents.
Wraith mask is a good start. Add 2 iron branches and your set. Just don't die, people who harass will be tough. With your blade fury, escape is key. Also you'll be able to fight back, with out magic kicking your but. I would suggest getting Aqua ring next. It's a cheap upgrade, plus your helping regen mana. Then start on your boots. Power threads are what I use, I like the AGI boost. Also the mana can, save your life.
I found survival is not always easy. Finding items to help, is ether based on health or mana regen. Having health is always good, and with jug, all you need in mana. Start off with Blade Fury, then ether crit or healing ward. Healing ward if you didn't get healing items.