The bigger house you can provide for them the better. When they play, they jump in the air and flit around in circles, which isn't possible in a traditional hutch. I let mine loose in the house for about a half hour a day, and a couple of times a week they go outside to play and munch on grass. Our yard is totally fenced, though they have found the wood pile to be an excellent place to hide out and scare me into thinking I've lost them. LOL
They have an average size house cage, but I know it's not enough for them. We're going to build a custom outdoor hutch similar to a chicken tractor, two levels, house up top with a pull out tray for cleaning, and access to the ground. We have a perimeter fence around the chicken house, so I was thinking about rabbit proofing the bottom and giving them daily access to that and locking them up at night. Not sure yet.
I got Flemish Giants, which need more space anyways than the average size rabbit, but I don't want to encourage the double chin fatness through lack of exercise. I'd like them to be healthy fat instead of inactive fat. LOL