Why am I building an airplane? I'll try and put some of my thoughts here but it's one of those complicated questions, like "why are you climbing Everest?".
I've always loved flying. One of my early memories as a kid was making cardboard wings with rope handles and jumping off my swing set trying to fly. I flew fighters for a living with the Marine Corps plus Boeing 727's with several airlines. I hated leaving the flying but family came first after all the airline bankruptcies. Flying is one of those activities that I almost hear music while I'm doing it. Of course, I don't actually hear music but it feels like the feeling that I think an artist gets when they're totally absorbed in what they're creating. I found that after getting used to a new airplane (usually after about 500 of hours flight time), when you want to take the airplane somewhere, you don't think about rudders and ailerons and elevators and throttles, you just go there without having to think about the how part. It sounds corny, but you become "one" with your airplane.
I love building things. I always have. I like the mechanical, 3 dimensional challenges, the physical part of working with your hands and the creative outlet of turning bits and pieces into something beautiful (in my mind, at least). I've talked to Paula about it and it almost feels primal, like something that's programed in my DNA. I also like a challenge when I'm creating something. Not many things more challenging than building an airplane in your garage and then flying it 200 miles per hour upside down several miles from terra firma.
I like saving money. Let's face it, flying can be expensive. Building your own airplane can cost less than a new car. A big part of the expense of owning an airplane is the maintenance. Only certified mechanics are allowed to work on certified aircraft. If you build your own, the FAA gives you permission to do all your own repairs. Another reason certified aircraft are so expensive is the liability of the manufacturer. Some folks estimate that the liability triples or more the cost of an aircraft. No liability to build into the cost if you're the manufacturer.
Building helps my memory. That sounds odd but I think it's the result of keeping my mind busy with challenging tasks. I don't have a way of measuring my memory improvements but I know it's happening. And it's improvements to my memory that I'm noticing, not just that things aren't getting worse as I get older. Names and lists and the location of my keys and glasses are all easier. Reading and interpreting blueprints are like crossword puzzles on steroids!