Check out this awesome House Rabbit Palace ! What a great idea. The tutorial shows the first version and ends with the more sophisticated 2nd edition. Sweet! You could easily make this by retrofitting an old bookcase. You could also make it wide and short instead to narrow and tall.
If you’re thinking about getting a bunny, please don’t buy one! There are tons available for adoption. For the Dallas area alone, there are over 5,000 rabbits who need a good home.