The only concern about Roddick would be... He is the biggest choker of all time when it comes to big matches... on that note... I will play Roddick small... It's still a great value!!!
At over 2-1 Roddick has to be considered a live dog. In past meetings Djokovic really hasn't proven he owns Andy like a Federer does. Roddick is playing fairly well and has steadily improved aspects of his game. Meanwhile Djokovic isn't in peak form. imo its tough to justify laying -250 +
The "x-factor" could be the weather. As expected its very hot and I believe this will aid Andy's hope of the upset.