We weren't sure what a cat tree should look like, so we had to defer to daddy's judgment. We have to admit it turned out pretty neat, and we like to spend a lot of time laying on it, scratching the posts, and generally showing our daddy how much we love his gift.
I don't know all of the technical details of its construction, but daddy explained that it was relatively easy to do. He began with a plywood platform, which he covered with a soft material. Then he attached 4 4" x 4" posts of different heights. He used some big pointy spiral things (I think they are called lag bolts) to attach the posts. He covered these posts with different things, but mostly he used a heavy rope.
If we had to make another cat tree I would have some suggestions this time. For example, we don't have anywhere to put our book if we want to lounge on the cat tree and read. Also, now that we are bigger the platforms can get a little crowded if two of us want to lay on one at the same time. But these are pretty minor complaints.
If you want to build a cat tree for your cats, and why wouldn't you, you can get some pretty cool ideas here. Your cats would really love you if were as nice to them as our daddy is to us.