I came across this online and thought it was so cool, I decided to build one as a first birthday present to my kitten. (he's spoiled rotten, obviously!) Mine is actually covered in a low loop utility carpeting. I admit, it is probably alot harder than the sisal rope, but I just thought it would look nicer. Mine is slightly different than the ones pictured: I did not do any additional boards on the bottom for stability. My kitty is very light-less than 10 pounds, so it didn't seem necessary. Also I made mine so it can easily be folded up again for moving. I did make a extra bed to go from the second-to-the-top step over to the paint shelf, but he never used it so I took it out. I also added a Fleece "hammock" that hangs in the middle, just above the floor. I got the idea from my local pet store-who has big cages with kittens in them. Then kittens are sleeping are curled up in what were originally ferret hammocks. I made mine and only had to show my kitten once what it was for and he sleeps there all of the time now!

Here are the links and below is what they wrote about theirs.

http://www.caws.org/ladder.html
http://www.nd.edu/~akolaczy/catladder.html

This home-made scratching 'post' is made from a four foot step ladder. It is wrapped in about 600 feet of ¼ inch un-oiled manila rope. Un-oiled sisal rope can be used as well. If you're up for the challenge of making one yourself, be sure to get rope that is un-oiled; oiled rope is toxic to cats. Several one-foot square Berber carpet tiles are used on the top and bottom plywood rounds, as well as on the top step of the ladder, covering the metal parts. A staple gun, a few carriage bolts, a drill, and several evenings is what you'll need to build one yourself. And typically, your cats will use it!
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Any questions about mine, pm me! I can e-mail you pictures, if you wish!

redphoenixx-thanks for the great cat ladder scratching post idea- my cats would love one!