I just built this with some modifications to some instructions I found on the Martha Stewart website. “It’s a good thing.” Most of the mods were to accommodate my larger cats…so I super-sized and also put in more structural supports.
It’s a two level cat house made out of two 18 X 18 cardboard boxes. There is a cut out for the cats to jump up on to the second level. The roof opens up so you can look in or so that cats can pop up and attack you in a surprise offensive.
Adding a back door in case the crazy kittehs knock the thing over onto the front blocking the main entrance/exit. Note: the thing is quite stable so this may not be a problem.
I also added some diy cardboard brackets supporting the ceiling of the first level. The original design does not have a lot of support. The brackets work great. I added six and the thing is so solid my 13 lb tabby can jump in without any breach in hull integrity. Also they provide a nice little architectural ceiling on the inside. I know cats appreciate this sort of thing.
I glued with some fairly liquid paper binding glue instead of a glue gun. This stuff sets quickly but did allow for moving/adjusting so I could get everything fairly square. I used bulldog clips to clamp the parts for drying. The glue is also non-toxic since I know that my tuxedo cat will eventually rip the whole thing to shreds.
Martha recommends cutting off some flaps on the top and bottom levels when gluing. Instead I glued extra bits down inside the boxes to add more support/stability.
I will likely cut out more windows. Next, I’d like to make some sort of cardboard cat tank that I could attach to the top of a roomba.