Here's something to add to the list of awesome things you can build for your cat: a catio. It's a portmanteau of cat + patio, and it's an enclosed outdoor space that lets your cat enjoy the great outdoors, without the attendant risks.
LOVE this screened in outdoor cat area. My inside cats would LOVE to be able to climb out a window for some fresh air Tap the link Now - All Things Cats! - Treat Yourself and Your CAT! Stand Out in a Crowded World!