1 person can't do all the stuff alone, unless we are talking about simple and straightforward game.
While I can code, I'm not really into the team-leading, and then there should be game designers, artists, modellers, animators, composers, more designers, etc...
Just not feasible for a game of this scope. Pretty sure whoever came up with the idea of UFO: AI wasn't told:
if you want it, do it youself. Period.