Yeah the class guide linked above is good. Scroll down a couple of posts past the guide and someone replied with some additions and corrections. Even as an experienced TF player and I've played a lot of TF2 already, it was a pretty good read! He's right about the sniper's worst enemies... as a sniper whore, I hate scouts and spies!!
And he's right that snipers shouldn't solely concentrate on sniping on the battlements in 2fort. Although when I'm up there, I primarily go for enemies dropping down to the bridge (if there isn't enemy snipers owning me), I tend to just play defense more inside the base around the main room with ramps and stairs and keep an eye on the sewers.