Please, please, please do not follow the advice given by the person above. Turning your rabbits loose is not free ranging it is setting them free, which is very illegal to do. Plus you take chances of them getting VHD, an extremely deadly disease that ha spopped in the US in the last couple of months, and they have no idea where it came from. Ferals are at extreme risk for it. plus its not ethical to set 8 week old rabbits loose! They can also be picked off by predators, and as mentioned disease. There are other diseases and parasites they can also pick up from local wild rabbits. not only that, when they breed, they can displace local wild populations and be extremely destructive. Here is one example of that. It is because of people that think its OK to let their pet rabbits run free. Providing they survive the elements, they can breed like crazy. Then you can end up in a lot of trouble with animal control over it. Because of people doing that, this university now has to find a way to exterminate. Now the animal rights groups want to pass a law in the area that bans the sale of un neutered rabbits. So if you think its ok to turn them loose like that, icw, think of who and what you are affecting. I know as a rabbit breeder I sure as heck wouldn't like to have a ban on them across the US(like they are trying to do in canada) because someone thought it was cool to let their rabbits run loose. And I don't want my herd getting infected with VHD because of it either! that is something that is not curable, and the government will step in and destroy your entire herd because of it. Free roaming rabbits are also not happy rabbits, since they are surviving, not thriving. I would never suggest to someone new to rabbits thats its ok to let them roam free. 
http://www.vancouversun.com/technology/fertile+rabbit+sales+SPCA/2960277/story.html
google vhd. you will come up with all kinds of stuff on it.
Now to answer the OPs questions. You can house them in the same building. Just not where the chickens can get to them. They can pass diseases back and forth like coccidia and e coli. Make sure each bunny has its own cage. And that the area they are kept in is predator proof. Standard all wire cages work the best. And if you do want to let them out on some grass, here is one of many proper ways to do it. Do not let them out of the pens. Tractoring pens are the best to use. Just make sure you supervise them so they can't dig out of them. all of my rabbits are kept outside in a barn, in cages. Each has their own cage unless its a doe with a litter. Dog cages make nice tractoring pens. Sometimes you can find the grid shelves at goodwill. They make excellent animal pens. That's where I got mine from. Thats my niece petting the bunnies in the photos.
http://www.facebook.com/photos.php?id=1587164212#!/album.php?aid=44368&id=1587164212
http://www.facebook.com/album.php?aid=44288&id=1587164212
http://www.facebook.com/album.php?aid=44288&id=1587164212#!/album.php?aid=43612&id=1587164212
thought I had some of the dog crates, but I guess not.
http://www.facebook.com/album.php?aid=37803&id=1587164212&op=6
One other thing not to do is to buy the cheapest brand of pellets you can find. They are often loaded with corn. You want a brand that is high in fiber, and low in protein. Two of the purina brands(show formula, and fiber 3) are corn free. Corn can cause bloat. Thats why you don't want them eating chicken feed.
Also, I breed my own, and buy mine from breeders that also show their rabbits. Sometimes i will pick up one or two from a local auction barn. The best place to buy them from are at rabbit shows.
They should also have fresh grass hay to balance off the pellet diet. Helps keep their gut moving. You will also want to get ahold of the guidebook to raising better rabbits and cavies published by the arba.  
www.arba.net . and storeys guidebook to raising rabbits. stay away from books provided by house rabbit society. Nothing but incorrect information that can harm your rabbit. Basically do as much research as possible before you get them. Also read up on diseases and how to check the rabbit for them. Some people will try to pass a sick rabbit onto you if you don't know what you are looking for. You will also have to self medicate them at one point or another too, being that most vets don't see them.