Do you need to buy a special roasting pan in order to make this recipe or can you use an ordinary one you have at home?

No special pan that I'm aware of. I have a ginormous non stick Calphalon turkey roaster that works well. You just need something big enough and deep enough to do as nutcakes suggested - one or two layers of tomatoes and sides high enough to catch all the juices when the tomatoes roast down. If you're doing a smaller amount - say 2-3 pounds, a 9" x 13" baking dish or deep casserole dish would work too.

I think the big roasting pan was called for because of the volume of the ingredients, so there would be room for pretty much a single layer and the sides are high enough to contain the bubbling juices. I'm not sure what you mean by ordinary roasting pan, but you could make this in 2 pans if needed or cut the amount of ingredients down to suit your pan.