Elite Areas with hero-only team (Both NM and HM)

So, people tell me that Elite Areas - Deep, DoA, FoW, Urgoz, UW - are doable by a player and her/his heroes team only, both in Normal and Hard Mode.

Ok, but how do you do it? Are there specific builds for such things? Do I have to be a super pro player? Do I have to sacrifice a black moa chick to Abaddon to do it?

I have been able (with a POOR hero team) to complete fow with ease with just heroes NM. I have completed parts of doa NM with just heroes as well. I have yet to try deep or urgoz, and did uw with a half group of heroes/half people NM.
Have yet to try any in HM.
I know there are builds for doing most of those areas with just heroes (I just do not actually know them nor usually use premade builds).

Haven't tried heroing any of those in HM but from a NM perspective it seems it's more a case of having some familiarity with the areas and being aware of the things that'll ruin you day rather than it being tough from start to finish. For example, FoW is trivial, though if you're fighting a group with three Skeletal Icehands it's a good idea to flag your heroes so they don't all eat a triple serving of Deep Freeze-Maelstrom. It's really easy to aggro half of the Burning Forest too, so be careful there. Otherwise it's not incomparable to a big explorable. As for the other areas:

-Deep has some tricky spots due to the environmental effects (again, checking the wiki beforehand will help you not be caught unawares), but it's largely just the fight against Kanaxai that's troublesome. Build-wise, you need a KD and sufficient party healing for the end fight. Other than that, whatever you would normally run (provided it isn't terrible) is fine.

-DoA has four areas, plus Mallyx. City and Veil are reasonably simple, though in the latter make sure you don't get rushed from behind when fighting the Lords. Gloom is tough on the first quest where you have to survive the huge waves of demons, though thankfully it's at the start so if you die you won't lose any progress. It's probably a doddle with Panic now though. Also be aware that when you kill the end boss it'll spawn a bunch more foes, which in turn spawn a bunch more foes. If you don't want 25 Earth Tormentors tearing your face off, keep away and pull conservatively. For that matter, careful aggro at the end of each area is important, but especially so in Gloom. Foundry is the only area which is persistently difficult, but again, Panic should make things a lot easier than when I did it. Don't forget to turn your lightbringer title on.

-Have only ever done Urgoz with others. In fact, I've also only ever done it in HM. The theme of big mobs continues. In all the times I've done it someone has been told to stay behind at certain points to prevent huge monster spawns ahead, though I'm not sure whether that's necessary or what exactly goes on. Check the wiki. As for skills, Edge of Extinction is particularly useful, not only in a general sense, but because Urgoz will kill himself with his exploding plants.

-For some reason which I still can't figure out, I have next to no interest in UW. I farmed smites a bit back in the day but I've never seriously contemplated completing it one way or another. However, in addition to checking the wiki (preparation is key), see here.

Overall, just have some familiarity with where you're going and jump in. They're not so difficult that you can't roam around in them and have some success. If you're comfortable with average level HM stuff like vanquishes I don't think you have a reason to be overly concerned.

As for HM, the only one I would expect to be disproportionately more difficult (i.e, putting aside normal HM changes like level and attribute boosts) is DoA due to brutal environmental effects and the Enraged monster skill. If you look around there are threads for this.