I was just recently given several hens and a rooster. They are all pretty big sized compared to the other chickens I have. The rooster is huge next to the Buff Orpington that I have. All of these chickens are solid black, with a green shimmer, and they have a gray colored legs, the rooster's legs are dark grey. Can anyone give me an idea what kind of chickens they might be?

Most likely they're Black Jersey Giants. They really get huge. Here's a site with pics of different breeds. Have a look and compare.

http://www.cyborganic.net/People/feathersite/Poultry/BRKPoultryPage.html#Chickens