Are you planning on cooking it the traditional way, then just dumping it all into the roaster to keep warm? Or were you planning on trying to cook it all in the roaster itself? I've never cooked dried pasta in a roaster, but it does cook up well in a pressure cooker. You just need to avoid really thick and/or sugary sauces since they will scorch, and add a tiny bit of water to the sauce for the pasta to soak up. You don't even need to boil a pot of water and strain the pasta.
If you're just using the roaster to keep it warm, just put it on it's lowest setting and add a splash of water and stir it whenever it looks a bit dry, should be fine. I wouldn't try and make it from scratch in the roaster though, that's going to take a long time and you run the risk of burning the sauce.
If you're going to be busy or in a hurry the day of the party, you could also make the pasta in advance and toss it in a little oil, then refrigerate it in large ziploc bags until you're ready.