I've struggled with this same thing, and in the end, I tie things that look like they're the correct size and ratios of height to width to length. You also need to make sure your hooks are the exact same type from the exact same company. A 1/0 hook from one company can be significantly different than a 1/0 hook from another company. I've also found it depends on your fishing style and the size of the fish you're going for. For instance, I target big largemouth bass, and use BIG hooks on my flies. A 1/0 isn't a big hook for a largemouth, and I go as big as 3/0. A lot of people use this same size for stripers that run 10-20 pounds. I don't size the actual fly as big as I would for stripers, I just use a bigger hook for the same size fly.
My passion for catching fish is eclipsed only by the fish's passion not to be caught.