So my knowledge of the 40k universe only goes so far and i've been looking for a good way to incorporate necrons into my campaign but am having trouble figuring out how. From my knowledge, which may be wrong or outdated, the necrons are beginning to awaken from their tombs but have generally only attacked other races when their tomb planets have been colonized? In the black crusade description of them however it seems like they are basically raiders in the screaming vortex, attacking planets/cities and harvesting resources from them, this i can work with but it seems to be not in the description of necrons that I am familiar with. If they are indeed raiders of sort in the vortex, anyone have suggestions on what they are accumulating resources for or a good way to put them into the campaign?

I think part of what the necrons are doing depends on your core timeline books; 3rd ed (IIRC, which I probably don't, timewise) they were just a tossout with a few models and without a real codex. They were interesting weird bad guys, but not an army. This is when they're attacking settled planets like you described.

Later, more of them wake up. Monoliths come out. They get a real codex. Tomb Spiders are scary. Now they're actively going back to their original master plan; killing everything that's still alive. Cause lets be honest, screw those guys.

Now, as for WHAT they're taking, I have no idea. I didn't think they harvested resources, they don't need any. They're all powered by green, and they don't build things as far as I know, so no idea.

I'd say that the easiest way is probably to make a Necron Lord with a bit more ambition than simply killing everything. Maybe he just wants to dominate the galaxy and completely seal of the Warp from the material realm?

As for what they are taking I would assume that they make most stuff out of metal so I could seem them taking what metal they can get their hands on and returning it to their base of operations for a purpose only known to the great GM. As to their plan it might be to return themselves back to organic bodies again or simply they're feed up with everything and have decided to wipe this galaxy clean of the pestilence of life.

The main problem with having them as an anti-Chaos force is of course that they would be stealing thunder from the Eldar who already are pretty much doing that thing, and that also goes for the mysterious enemy without a clear agenda. Just random raider could be fun but rivalling Chaos followers would probably work better in that regard. So its true that the Necrons don't have many clear-cut spaces left for them. One of the possible ones could be to represent a Great Evil if the characters are getting tired of being the bad guys you could throw them at an enemy who is even worse than they are.

I would look at the assaults and raiding from a different perspective.

The first Necron "scouts" just woke up and are trying to get their bearings. They need to figure out what has happened during their slumber and what the new "enemy" is like. The Necrons don't die like we do, so they don't view things the way we do. If they "lose" a few squads in a battle they haven't "lost" they have just obtained information on the enemy.

I think it's akin to one of us poking an ant hill with a twig. Once we figure out what happens when we poke the ant hill, the ants attack the twig, we throw the twig aside and forget the twig existed. The next time we see another ant hill we pick up a new twig to poke it with. For us the whole thing is a non-event, for the ants it is nearly cataclysmic.

In the case of the Necrons, we are the ants.

I think Itsuncertainwho has an excellent handle on it. The Necrons just want to kill everything because of their bad childhood as a race. Chaos is near the top of their list because it's such a big threat and they are really opposed to psychis powers and the Warp. The necrons are about the purest anti-chaos there is. The Eldar and the Grey Knights etc use psychic powers so they're basically trying to fight Chaos with Chaos itself (in the latest codex there's a Grey Knight character who uses a daemon weapon, thanks Matt Ward). The Necrons are in the completely opposite direction, they make their own alternate dimensions run entirely on physics/geometry kind of on the other side of real space to the Warp (you know, in a 12th dimensional way). Reading the background for Abaddon's 13th Black Crusade it looks like the Cadian Gate exists because of Necron Technology.

This last point opens up some interesting options for a 'master plan' for your Necron Nemesis. Maybe they're trying to 'stabilize' the Vortex. This would be really bad for any heretics living there as that cuts their connection to their gods and any deamons they have understandings with. Best case scenario the storms all calm down and then they're probably looking at an Imperial crusade driving into this newly open region. Worst case the Necrons pull off some real techno-sorcery and entirely suppress or cut off the Warp from real space in a set region. This means no psychic powers, no interstellar communication that doesn't take years for an answer and no Warp travel. That's probably something the heretics would want to stop.

Or if you want smaller scale, one of the coolest things about Necrons is they're basically robots that used to be people. Bitter, vindictive people who were mentally downloaded into unfeeling robot bodies and put in unstable suspended animation for millions of years. Most Necrons basically are just robots, but the lords still have personalities, and if they weren't twisted and insane to begin with they sure are now! You can play a Necron lord as a completely crazy genocidal psychopath with control of the most powerful and advanced weaponry the galaxy has ever seen. Maybe his body had some basic programming to make him fulfill a specific role, but over time that programming has been corrupted or his own force of will and plain crazyness have subverted it. He may not know what time it is or even who he's fighting, he just has some goal that he's compelled to fulfill. This could be policing the borders of Necron territories that haven't existed for millions of years. It may be collecting examples of the most dangerous warriors and beasts in the area to assess for weaknesses. Maybe he just makes up missions on the fly and pursues them with exteme prejudice. If you want to give him an overarching sheme to complete, fine, or he can just have a wire (technically high-tech solid-state connection) lose that shorts out periodically and he just resets to a new set of commands.

Well, there are various ways to run the Necrons... First of all If you use the old codex or the new.. or something in between... If they are simply the will less slaves of the C'tan they are either going to be and invasion army that needs to be defeated or something terrible that lurks in the shadows, maybe they are trying to fina and wake a major tombworld..and must be stoped, least they succed. But either way they are likely to be a silent unbending army who will meet diplomancy, intrigue or taunt with utter silence down the barrel of a gauss flayer.

In the newer codex they are much more diverse -some are even willing to work witth the forces off chaos - and prone to infighting (even if greatly limited by their command protocols), plots and all sorts of quirks... They can have various differt agendas..

But generally from my point of view Chaos is the one great enemy in the eyes of the imperium, the constant looming threat, Sure the orks are everywhere and would probably be unstoppable if they couldn unite but they can't, Tyranids are beyond number, but somehow they seem like something that far away and always seems to be beaten (at great cost, granted)... but from Chaos point of view the necrons might be the thing you consider the biggest threat, they can't be corrupted and bend, there are no place to tear..And the deathless robots cleans up chaos and wipe out life... life being one of the thingss that gives chaos power.. Immortal, enormous numbers, best tech and meticulous and anathema to the dark gods, the necrons might very well be considered the greatest enemy of the ruinous powers... Maybe even my all...

Deathwatch supplement The Outer Reach has lots on Necrons. Some of it is definitely applicable for Dark Heresy.

Tome of Fate also has enough to work with.

The overarching fluff of the Necrons basically ignores the small scale, exploratory raiding they do in favor of focussing on the monolithic (pardon the pun) offensives they pull.

When the Necrons get busy they do it like the tyranids: either Hive Fleet Behemoth scale unstoppable killing machines without end or Hive Fleet Kraken style wide raiding and intelligence gathering followed by exploitation of vulnerabilities.

You usually see the Kraken model when the hive worlds are just awakening, which is what I take the status of the tomb worlds in the Vortex to be. You see the Behemoth model when everything is awake and the resident Tomb Lord decides to drop a series of monoliths on someone.

Here's how I'd run it: You have all these Tomb Worlds just starting to wake up, and they send out some exploratory raiders. They start out small in numbers and relatively easy to handle, but Nurgle-marine resilient. More annoying than anything else. Then they start performing recon-in-force, and the Warriors show up in Horde scale, with Destroyer and possibly Scarab support. At this point, players should be saying 'okay, this problem is getting worse. Investigate or ignore?' If they investigate, then adventures as per normal. Either way, the nature of the Necron juggernaut being what it is, eventually you reach a scenario where great Tomb ships are advancing slowly across the Vortex, wiping out the pirates of the Ragged Helix and ending the war in the Hollows, permanently. At this point, the players may be going for a midnight ride to shout 'The Necrons are coming' to any world that will listen, and may try to build up a loose coalition of forces to fight the oncoming Juggernaut. Think Mass Effect 3.

If they're particularly cunning, they might try to lure the Tomb Fleet towards Port Wander and watch Battlefleet Koronus get wiped. From there, it seems likely that the Tomb Fleet would move into the Calixis sector, cutting the Achilus Crusade off from reinforcement and forcing the Imperium to fight back- and leaving the players to pick up the pieces and capitalize on the- ahem- chaos.