You couldn't have taken a random black dragon, increased it's size... Gave it more texture, etc? Heck, you could have taken the current model of Deathwing and modified that.All of those were possible courses of action, sure, though I suspect that using a different existing model would likely had the same result. Slight modifications to an existing model may not even have been noticed, given the light show going off in that scene. Also, as others have pointed out, he was already wearing the armor at that point. In the end, we're currently having a long discussion about a single model which appears for a few seconds, and is wreathed in gold lightning for much of that time