How do you make a model volcano?

Its for my 7th grade science project and i have to make the three 8in.x8in. volcanoes (composite, shield and cinder) but I dont know the materials i need, i just figure to make it explode i'd put 7up with red food coloring and put mentoes in it, but i dontkno what materials to use to make the basic shapes. i thot about paper mache but i thot that would be alot more work cuz u need the wire and everything for the basic shaper but what would be the best material for it?