a self sufficient refuge camp is pretty much a city. It will have to provide it's own food, water, medical support, shelter, and most importantly logistical infrastructure to manage it. I'll focus on only on the most obvious issue, food.
The only way for a refugee camp to provide food is to grow it or hunt for it. The number of refugee's involved in your average camp is so large that hunting and foraging would be insufficient to feed them for long, you would kill all the game. Thus a self sufficient refugee camp is one that grows it's own food. Were talking about farm land, lots of farm land, and year or more from beginning to set up farm before your first crops can be harvested. Before you ask raising animals is actually less efficient then raising farmland. It makes sense on certain types of land where traditional crops don't grow well, but if you assume land that doesn't support traditional crops all of this becomes harder and a longer en devour.
In reality growing your own food isn't that easy. It takes, very roughly, one acre of land to produce enough to feed a single person (though refugees would likely be willing to survive on a little less). still were talking about 12,000 acres of farmed land, or about 18.5 square miles of fertile farmed land. Actually, that's how much farm land we need with modern technology and tools, the amount of land increases if you are doing this without modern technology and techniques used by first world farmers. The actual amount of land needed is MUCH larger then that, not all land can be farmed, some of the land would have to be devoted to housing, roads, and infrastructure, etc etc. in other words 18.5 is a extremely generous understatement of how much land would actually be needed. That's allot of land to find in the middle of a warzone or disaster area, and that's assuming all the land is fertile!!
There is also the effort and infrastructure required to get your refugees to learn how to farm land and distribute the results. Just teaching novices to farm land remotely efficiently would take at least 5-10 years. Really probably much more, but I'm being quite generous with these estimates to prove my point.
In short you would need a huge area and extensive time and organization just to address the issue of food. For the first 10 years you would still have to be shipping food to them while farms are built and farmers are trained. This is ignoring the real time consuming issue of infrastructure and logistics it takes to do something like this. Trying to organize a bunch of untrained and scared refuges to do something like this is an...astounding challenge I can't begin to estimate, but it's definitely a significant factor in all of this which shouldn't be ignored.
People don't live in refugee camps for years. These camps are designed to be quasi-temporary as people are moved out to other areas that can sustain them better. The camps may last for awhile, but only because new refugees keep showing up, even as old ones are moved on to more perminate locations. the refugee camps is the thing that exists while we figure out how to ship people to wherever they will be setting up a new city.
So the real question to ask is how hard is it to build a city from scratch, and then start shipping refugees there. During the original building of a city it's easier to not have all your refugees, more people means more logistics keeping them all alive and more overhead. Instead a select few with skills could be sent somewhere to start building, and slowly more immigrate in to the land as more farms and housing build up....it's a city being built.
And finally, of course, someone claims pretty much all fertile and livable land. Finding any land on the world large enough to support people is not easy. GETTING people there is not easy either, unless you happen to own the exact spot of land where refugees are congregating your need to set up transportation to get them there, and while their waiting to be transported your have...a refugee camp lol. these camps are only designed to last as long as it takes to figure out where to send refugees and how to get them there after all.