You say you don't want to get into the technological stuff, however architecture contains a LOT of maths and physics. If you want to do roller coaster designing, yes you'll need good design skills, but you'll also need a working knowledge of maths, physics, engineering and possibly even business management. There really isn't a vocational degree you can do that will lead you straight into it. However, I do wish you the best of luck!
EDIT:
I just found this website for you. It's an interview with a rollercoaster architect. Read the last paragraph especially:
http://www3.nsta.org/main/news/stories/science_teacher.php?news_story_ID=49270