Newbie question - Tin roofing sheets in with shred?

Hi everybody, first I want to thank all the regular contributors for all the info on the forums that has given me a good scrapping education so far since I registered last week, and more pointers that I expected to find.

So as a newbie, here's a basic question. At what point (weight) does tin (I have almost 100 lbs of roofing sheets and access to more) become better to separate out of my shred pile to sell as its own category? Is this ever done in smaller amounts? I have tried to contact my 2 yards (only ones for 40 miles) about it, one is impossible to get on the phone and doesn't answer email, and the other isn't very newbie-friendly but sometimes has better prices. I'm just trying to win them over showing that although I may not be a very experienced scrapper, I can at least be an educated one.

Thanks for reading, and I look forward to meeting all in the posts. Now that the rain has stopped here in Middle Georgia, the wife is settling the baby down and reading her nook leaving the keyboard free for me to learn more on SMF. -Drew