A propane fire pit can undoubtedly be used to roast marshmallows. You can roast marshmallows in the same manner as you would over a wood-burning fire pit. To roast them securely, use roasting sticks that are as least as long as an adult's arm. To roast marshmallows over a propane fire pit, simply poke them with a roasting stick and place them over the flame. To toast the marshmallow evenly on both sides, rotate the stick frequently. Continue cooking until the marshmallow is light brown all over, then serve.