A roasting pan is a pan that is designed to withstand high oven temperatures for a long-time. It also better be pretty big and strong to hold turkeys, chickens, hams, or roasts with lots of vegetables. Often the roasting or roaster pan will come with a cover and/or a roasting rack.
The first decision you have to make when choosing a roaster pan is whether it will be disposable or not. Many people opt not to store the large pan when they aren't using it. If they are preparing a turkey for a church supper or family dinner they prefer to take a disposable roaster pan. They have the advantage of not cleaning it and lugging it home.
Disposable roasting pans come in handy when you've only got ONE roasting pan and you're cooking a turkey AND A ham for the family reunion. It cuts down on anyone forgetting to bring an extra roasting pan for you to use. One less thing to go wrong!