Sasami mentioned a good point.
I know of people who use the cage only to put their rabbit some place safe when they're not home, or at night when everyone's gone to bed. Thus, the cage doesn't need to be very big, just big enough to stretch out in, and still have room for food and water.
Sometimes, though, people don't get to spend a whole lot of time with their bunnies, so it's better for the cage to be a lot larger, with room for toys and such.
It's estimated that for each pound your rabbit weighs (or 1/2 kg), you should have at least 1 square foot of cage space, as a BARE MINIMUM. For instance, Mini Rex grow to be about 4 lbs, thus, the minimum cage should have 4 square feet.
There are many different cage types, some that have wire floors with pull out trays underneath to catch droppings, some with solid floors, some with room for litter boxes, some with a combination of each. If you decide to go with wire floors, you will want to make sure that your rabbit has a place to rest his/her feet so that she's not always sitting on the wire. If you decide to go with solid floors, by having either a piece of wood or drywall in the cage, this will also help prevent sore hocks.
There are lots of rabbits than can live outside year round (provided that they are protected from the elements), and all rabbits can live inside, if you've got the room.
What kind of rabbit were you looking to get? A mixed breed or a purebred?