These are our pets, Buddy the Dog and Melon the Cat. While they get along just fine it was important to give Melon a space of her own. This also helps by giving us a place to hide her cat stuff people dont want to see. Perfect space is the closet under the stair well. But how to keep that space assessable to her and not the dog... Cat Door! Better yet it took ten minutes and was free.
Step 1: Find a Space
This closet space was great to keep Melon's litter and other cat things in.
Step 2: Measure Cat Door
This step will vary depending on your need. This door is just big enough for Melon. Buddy can fit his head in but when he does he usually gets a pop or two. She feels very safe in this space and always has somewhere that's just hers.
Step 3: Cut Opening
After measuring I used a simple oscillating tool however you could use a key hole saw or even a utility knife, drywall is not hard to cut and the cuts dont have to be perfect because they will be trimmed out.
Step 4: Trim Out Door
Find a scrap piece of trim and cut to size. As you can see in mine I used a few different styles I had laying around. I simply used hot glue to attach them. We added a little name board for flair. Now you cat has an easy free door to a space to call their own.