I once tried making a game engine from scratch. I tried writing in Java (I can already feel the disapproving sighs). It was 2D and ran at 12 FPS (at best) with only 7 objects on screen. My collision detection was horribly off too. It was the most haphazard piece of crap that I had ever tried to write. Unless you're goal is to make a game engine for the sake of practicing your programming, go with a pre-made one.