Baldur's Gate : The Sword Coast Chronicles : NWN2 Persistent World

How would you structure a concept like this?

CHAD!!!! Come show this person the way! Seriously...there is a monk build that is insane but you have to deal with the no HIPS until like level 27.........

depends on how much Monk you want to be vs. how much rogue. The 'standard' that many players like is M11/R10/A9 for 10d6 sneak dice + Crippling Strike and Epic Precision. Gets 15 APR (16 with haste) due to PTWF and the bugged 1 extra attack from flurry of blows. 16 is the threshold that gives you a 6th attack in the first flurry (which is the flurry that counts for sneak attacks coming out of stealth). It's a fine build type, tried and true and will work fine.

The character I play is credited to either matelener or MrM3ntalist, or maybe someone else who came up with it and doesn't get HiPS until level 30 (and no I did not RCR into it, I used a belt of mischief for feint along with blinding strike to land sneak attacks and spent most of my time in the Upperdark leveling where feint works fairly reliably.) This would be R16/M3/A8/NWN3 which, admittedly is far less of a monk then a rogue, but get's 13 APR which is enough to have 5 sneak attacks out of stealth. Each attack is good for 14d6 sneak damage which makes a lot of enemies dead after the first flurry. The ones that survive have to save against death attack 5 times, plus save against blinding strike when it's active so there is a pretty solid chance of killing or incapacitating the enemy before they can react. It has epic dodge (which is why it can't get A8 for HiPS until level 30 due to 3b20 rule) so if an enemy lives through the first flurry you have adequate time to escape, and escape you must. This build is the type of character that might say something like "I can't teach you how to fight, find a warrior for that. I can teach you how to kill." Basically when you attack out of stealth you kill stuff...fast. However, if you don't manage to kill something you better have an escape route ready! In fact you better have multiple escape routes and you also better know what to do when some Revenant see's through your stealth!

TL;DR - The build Calodan is referencing is fun as heck to play once you reach 30, but is a PITA to get there, requiring patience (especially if you're like me and can't take questing) and a lot of planning and figuring out where you can go to level when HiPS is not available. For the journey, the build I outline is a really bad idea, for the end result it is a frigging wrecking ball of destruction.

Bombs might make the experience a bit less painful, by the way. That said, my personal recommendation would be to go with the standard build which does a bit less damage and loses Epic Dodge, but is far more playable 1-30... If you want more sneak dice, you could simply go R19/A8/M3 which only loses some speed and 1 BAB from the 3 levels of bodyguard while gaining a feat at R19 and being able to get HiPS earlier. Extra speed is really nice though.

EDIT: Completely neglected to call out that with you the changes to Hide in the Shadows, which is granted to Rogues for free at level 7 and improves up to level 21 you could go R27/M3 or R24/M3/NWN3 and use that in place of HiPS. Just realize until you reach R18 you need to get some distance before activating it so you have to pay attention to where you are... Doesn't include Assassin the class, but would have very similar damage with more skill points so worth consideration.

EDIT 2 (sorry): You of course could also go M20/A10 which has less sneak damage, but could be decent either as DEX based dual wielder or a fist monk. Would need DEX, WIS and INT and would basically strike from stealth and/or use stunning fists. 8 APR with Greater Flurry (bugged extra attack) so even with haste wouldn't get enough attacks to reach 4 death attacks, but 3 with fist damage is pretty decent. Could even use Northlander Hewing to reduce APR to 6, 7 with haste (needed to retain 3 death attacks out of stealth). Max damage on monks fist is a pretty hefty increase to damage, making the damage from assassin more gravy than anything. There is also the Monk of the Long Death kit which gets it's own death attack (kinda) similar to Assassin, so you could go Monk 30 or M22/A8 or M21/A9 with the MotLD kit and be a Monk/Assassin that way.
So as I said, depends on how much of a monk you want to be....

I would go Monk 11/Rogue 11/8 Assassin.

If you are going for monk/assassin based on SAs, then just 3 levels of monk is enough.

Monk3/Assassin8/Rogue16 is great build with good saves, AC and damage - A lot of SA dice and 5 attacks on the 1st flurry.

On the remaining 3 levels you can either get another 3 levels of rogue for more SA and an extra feat, or if you are patient enough Bodyguard for bonus AB, speed and will saves. The problem with Bodyguard is that you get hips at level30 if you want to get all the rogue epic feats. For me, the best SA/Hips build.

And here is something different: Monk 20/Assassin 10, with a focus on wisdom.

You have Íntuitive Strike to get wisdom modifier to your fist AB. You have Zen archery to get wisdom modifier to your shuriken AB. You can go for both Fiery Fist and Blazing Aura to get extra fire damage with each hit. You will have rather high-ish Stunning Fist DC, and you can eventually use HiPS even if you rely on on Intuitive Strike to level up. The Assassin spell book can give you some minor perks too, for example that True Strike spell can give you a considerable AB boost and make your eight unarmed attacks per round something nasty, even without the added sneak attack dice on top. Not to mention that with just 17 dexterity, you can get Manyshot and use it with those shurikens to get up to 30d6 sneak attack dice with your first attack flurry, six rolls to paralyze, all thanks to those extra three attacks you get from Greater Flurry of Blows. Also, when you team up with other people, you can use your monk speed to flank enemies.