An unusual plan, but why not? The difficulty might be knowing which parts to buy and which to pass over, until you've got a good picture in your mind of what you want to end up with and making sure they will fit the frame you finally choose. However, when I've upgraded a few bikes in my collection I often find I have a pile of perfectly good displaced parts, say a pair of wheels, a chainset, brakes, gears and saddle and then start looking for a frame in my size to hang them on. It rarely works out that neatly and I usually finish by replacing some of the "original" collection of parts to match the "new" frame - then start again with a new collection of parts looking for another frame!