This is actually my job. And there are multiple answers. The best is, anything you want. Do the pre-reqs necessary to get into architectural programs (and maybe a couple other courses similar to those pre-reqs so you're not just doing the minimum) and then go study whatever will make you a happy, well rounded person. Sure, your job will ultimately be designing buildings, but you will also be talking with clients, coworkers, and making tough decisions where there are no right answers, so pick a major that will help you with that.