Re: Ursa Item build
I build ursa as:
PMS + Stick + Phase -> Vlads/Vanguard -> Dagger -> Hex
Throw a BKB in there if necessary.
The first stuff should be obvious, vlads if you're foresting, vanguard if you're laning, either of them will allow you to do Roshan and give you a form of regeneration. Dagger should pretty much be a given, although Lothars can be fun, Dagger is just cheaper and harder to counter. Also, Ursa, unlike SF cannot feasibly farm up a 15 minute lothars and then stomp the game with it in most cases.
Hex is where it gets controversial, and most people would build a heart there instead. The way I see it, if stuff is still insta-dieing to you come 30-40 minutes into the game then you've probably won already. People SHOULD have either a stun, or a slow, or an escape or (most annoyingly for Ursa), a GHOST scepter and this stage of the game, and you'll struggle to instarape things like you did before. Sure a heart will make you do more damage and make you harder to kill, but it doesn't fix any of these problems for you.
BKB will solve stuns, particularly if your team has enough disable, but even then you still want some item AFTER that. Until you've experienced the true horror of a Guinsoo + Dagger bear I guess it's hard to understand how evil it is. It renders everything but raw HP & armour useless against you, even BKB is hard to cast if you're blinking from fog and hexing instantly.
ONCE you've made these things you can consider a heart or an MKB (vs wr and suchlike), or possilby even S&Y (cheap, damage, -ms, hp, attackspeed for when your overpower is down), but I really don'ot see how any of these items would come above hex in order of priorities.
So yes, your build is very viable, and in my eyes the best build for ursa.