I very rarely make the same pattern twice, although I have done multiple log cabins or whatever, the fabrics and end result is always very different.
I learn while doing, usually I've learned enough to make my "ok" quilts into great quilts, but I'm ready to move on to the next project and so keep in mind what I've learned and do something different. I have been thinking of doing several series quilts, similar but different enough to suit me while I explore different aspects of a project.
So if a project has been designed for a king size, I'd just make the king sized first. You do have to watch some design issues when going so large because tiny little pieces will ultimately mostly be lost in the overall size. You simply cannot scale up a wall hanging to look correct as a king sized unless you have a football field sized bedroom and can get that far back for the same perspective.