Your first question about this build probably revolves around whether this will acutally work and if so, how. Short answer: It works because of Zed's W and because of the interaction between the Items themselves. The long answer will be given throughout the following Chapters. I will use the rest of this Chapter to answer your second question: "How did you even come up with this?" Well the answer to this is quite simple: Pure bordeom. I was thinking about different "unusual" Items in League (such as Death's Dance) that have a cool mechanic, yet don't see play that often, which filled me with determination to create a guide relying on said "unusual" Item. This Build is not 100% Champion Specific; You can build this on some other AD based DPSing machines like Riven, Panth, Olaf and so on. This Build also works on other "Assassin"-Type champions such as Talon or Riven.

Pros

+ Tanky as hell + Decent burst + Great late-game + Snowball-y

With this build you will become a super tanky, yet super bursty threat to the enemy team. This build scales great into the mid/late-game, but does not have to sacrifice any early-game prowess to achieve that. Because we run a set of offensive runes and masteries, our early-game is just as good as the any Zed's early game.

Cons

+ Prone to negative snowballing + Less burst than a full AD Zed + Mediocre poke

This build is very prone to negative snowballing, i.e. making a mistake in lane and falling further behind, than you would with your usual 08/15 AD Zed build. Since this is a more tank-oriented build, your burst is not as good as the burst of a full AD Zed. That means, that you might not be able to 100-0 the enemy bruiser. Also, your poke is really ... meh, so you won't chunk 3/4 of the enemy adc's health with a W-E-Q Combo.

First things first: This build will make you incredibly tanky compared to any other Zed build. This will make it much harder for the enemy team to kill you, since you're stacking a lot of health paired with a lot of Armour and Magic Resist to survive even the greatest of hits. To top that you get ! This item is your bread and butter. "But why is this item so extremely good?" You may ask. Well, there are several reasons why Death's Dance is more than beneficial to this build.
On top of your extreme tankiness, this item takes 12% of all damage deal to you and deals it to you as a bleed over three seconds. With this passive, you do no longer give a toss about being caught or anything like that. If you get stunlocked, whilst having this item and some tank items on the side, the enemy team will not be able to burst you down at all. Its other passive heals you for 12% of all of your physical damage dealt (though AOE damage has an efectiveness of only 33%) and since you will almost exclusively deal physical damage, the amount of healing you will recieve from this single item is immense (hence the optional Spirit Visage to further boost your healing).
The second item that makes this build is . This item's damage scales off of you maximum hp. That means: the more health you get, the more damage you get. On top of that, [titanic hydra size=30] synergizes extremely well with , since it deals physical damage and will thus heal you. With the %max health scaling and the heal from that, you can see as an in-combat .

Building tanky always makes for an easier time playing, since you won't get one-shot by anything. This will allow you to have a less stressful Zed-experience and is a great way for newer players who want to get to know Zed a little better, which means, that you can probably qualify this guide as newbie-friendly.
It's not the tankiness alone that makes this build easier to play than any glass canon build, though. It's your whole playstyle that's easier to adapt to from scratch. If you ulti into a fully grouped enemy team, you won't be stunlocked and instantly killed, since you are really tanky and have your . If you then find yourself not being dead in the middle of five enemies, you can pretty much just spam your spell and autoattack anyone in range and let heal you to almost full hp again.

Maxing first seems the way to go. This allows you to poke, farm from a distance if needed and it also increases your damage output by a significantly higher amount than maxing first would.

We max second, because this increases our total damage for a full combo by quite a chunk.

Maxing last is definitely the right thing to do, since this build in particular doesn't benefit as much from the bonus AD buff. 's cooldown and energy cost also don't matter enough to care about maxing it second.

, since a big part of our damage comes from our spells, of course and we don't really get the AD to support them through sheer scaling, so this mastery will boost our damage output just enough for us to notice.
Since we are melee, we benefit greatly from . The increased damage taken is also not a problem, since we are going tanky anyways.
I like to go for , because this boosts our sustain by quite a bit, but you can also spec into natural talen, if you want a little higher damage output. You usually won't be able to notice the overall difference anyways, though.
is self-explanatory. We are an assassin, thus our goal is to kill as many people as possible, and benefiting from that through a mastery? Sounds about right.
Is the perfect mastery for Zed, since it gives us a small movespeed-buff when roaming. You can swap it out for savagery though, if you don't feel confident in your farming-skills.
The rest of the tree is just basic Thunderlord's stuff. Nothing fancy about that.

Runes are completely based on personal preference. For glyphs, you can also take either or .The only more or less viable option for marks, apart from is the greater mark of armor penetration. For seals you can get , if you know, you will be facing an AD-Champion mid.
With this set of runes, you guarantee a strong early-game (AD marks and Quints) but also a good scaling into the late-game (per level seals and glyphs)

Boots are completely situational. If you are against a heavy-cc-team, buy , if the enemies have a bunch of slows, buy . You have to decide, what pair of boots is good against the enemy team.

As mentioned before, is just the perfect fit for this build.
It provides us with great survivabitly through its passives and with some damage on the side.

has been mentioned before and I don't have anything to say, that I haven't stated before.

is just overall a nice item on Zed. It provides you with a lot of cooldown reduction, health (> ), AD and a nice armour shred as its passive.

synergizes well with our already high sustain and also provides us with some more cooldown recution, health and on top of that gives us a nice boost on our magic resistance.

is a more situational item, but you will more often than not find yourself buying it in most of the games. It provides you with a nice boost on our armour, health and some extra on-hit damage and movement speed on its passive.

The one item that barely made it into the top 6 recommended items is . This item is really strong in this build, since it provides you with some extra sustain, damage, magic resist and a crowd-control removing active effect. However, this item is not as defensive as can be. So, if you don't find yourself stunlocked every fight, you will probably be better off with buying a or any similar items.

The only two core items in this build are and . Everything else depends on personal preference, your team comp and the enemy team.
Getting kited a lot? Buy and forzen mallet.
Is your team lacking crowd-control? Get a .

When playing tank Zed, you are no longer there to only keep the enemy carries from playing the game, you are also a - who would have guessed it - tank.
Usually on Zed, you start a teamfight off by ing the enemy carry and proceeding to killing them in one second with a swift > razor blades - combo, but now, you will be there, to attract the enemies attention.
You are now the one who jumps in and makes the enemies use all they have on him in an effort to kill him. The only problem the enemy team will face is: They can't. Once you are dropped to about half your hp, just spam your spells and basic attacks and heal yourself up, with all that sustain you have now acquired.
Congratulations, you have now killed the enemy marksman, made them use all their cc on you and yet you still survive.
That is what it's like to play tank Zed.