I would love to have written Roger Zelazny's first five books of 'Amber.' What a great idea he had about the shadings of reality!
I enjoy worldbuilding very much. I generally start with an approximation. With 'Flesh and Spirit' and 'Breath and Bone,' because I was thinking of a world on the brink of a dark age, I began with the sense of Roman Britain. But I purposely set the geography to match something other than Britain - which has been overdone.
I'm a fairly ordinary person - a lifelong reader, a former software engineer, and former math teacher. I come from a wonderful family of teachers, musicians, librarians, and engineers. I think I surprised them as well as my friends and coworkers when I took up writing as a hobby and let it take over my life!