I have cats. Lots of cats. Mostly handicapped or elderly; so they don't go outside. Still, I wanted them to have lots of fresh air, so I had a screened in porch built some time ago, connected to the house via a tunnel and a cat door.
I used a great product made by a company called "2x4 Basics" in order to build platforms that even the most crippled of the cats could easily jump up onto, and continue to climb in steps until they are up fairly high. They love it out there.
Today, I got an email from the company telling me that they had added a photo of my idea to their customer ideas gallery. I'm rather proud of that. It was my first large building project, and it turned out well. At least the cats haven't complained, or if they have, it hasn't been to me.
Since then I have built several other cat friendly projects (some of which are more "cat proofing" than they are cat friendly), and will post photos of them as time permits. Having pets has its challenges, especially when you are up in the double digits, but I find it is one of the most worthwhile activities in my life.