here is herman's cage a few months ago, some things have changes (like he has no blanket down now) and his level moved sides, another water bottlewas added, he has a box normally in there to hide in,and he got a larger litter box, he was the size of my mini lop in the photo (so around six pounds) this was my golden's kennel until he didn't need it anymore (i can get you the measurements later if you want for a comparison):
hermans level is a grooming table i used when i bred/showed rabbits(you can normally buy them from vendors at a show, a breeder on the board *might* know a website that sells them), it latches onto the side and he loves it. but i have a friend that has a grill rack (one that you would toss over a firepit to grill veggies and stuff) that is in her cage, it is covered with a piece of carpet like mine is (in the photo it is a piece of towel, but it is carpet now).
it is a little small, but he doesn't seem to get terribly cramped. and he is out only when i am home and winnie is penned (as up till yesterday he wasn't fixed). i think the key is that he has toys in his cage that keep him busy, he loves to roll the easter eggs around (they have a small nut in each so they make a noise).
another option that i LOVE is the puppy pen. winnie has only jumped out of it once and that was because i put a box inside of it tall enough to let her jump out, i think mine only cost me $75 and winnie is in a6 ft by 2 ft cage with it:
i love it because on nice days i move it outside for a few hours and it folds up, gives her room, and i can put it in a bunch of shapes and sizes.