I looked for something that would be big enough for my cat.  He's 15 lbs. And no he's not overweight.  Just a big cat.  I worried the box and smaller platforms would be too small but he loves to play on the two large and sometimes likes to squeeze himself into the box up top.  I liked that I could stain it to match my furniture and plan on adding some material to the platforms to help him move on it better.