I had asked a friend about this, as she has kennel runs for all of her dogs. She told me that if she has a dog that is spending any length of time in a kennel that 10'x10' is the smallest that she would go, but that even that in her opinion it is far too small. After speaking with her I began to look into doing 10'x20' runs.
I like the set ups that one of my other friends has for his bulldogs. Very large runs (most bigger than 10'x20') with raised dog houses and ramps that lead into the dog houses. They also have different levels and footing in there (some pea gravel, and some the boulders that were naturally in the area). He always keeps a kong in with his dogs. But I think that the different levels in the runs, and the different areas of footing, keep his dogs from getting the typical bad habits that kenneled dogs can have. None of his dogs are big barkers, and frankly are generally quiet when you walk through his kennel. They also don't pace. I think that pacing tends to happen with dogs that are in thinner and longer runs because they don't have much space to do anything other than pace. Plus with the different heights/footing it keeps them from getting into fence running and other such bad habits.
I also like the Doc Bobs at Tractor Supply. One of my friends has one and it's a really nice kennel. I think you can also get privacy pannels for those as well, so that your dogs won't start fence fighting each other. I would definitely also suggest some sort of top/roofing so they can't go over. Of course I also suggest a pad locked privacy fence surrounding your yard so that looky-lou's don't know that you have dogs there that they can mess with. Plus that way your dogs can't see anything outside of the yard, so that way they can't load up on something, thus developing barrier aggression.
"All changes, even the most longed for, have their melancholy; for what we leave behind us is a part of ourselves; we must die to one life before we can enter another." -Anatole France