Dakukaruma

So hey guys i'm slightly confused as what sort of relatively cheap materials i could use in my Foundry project the names Ceramic,Graphite and refractory all pop up i have explored all of these thoroughly and have concluded that graphite is very efficient for being able to withstand heat and refractory materials are good for insulation but i seem to struggle with picking an appropriate material to make the "Outer Shell" of the foundry (Furnace) Out of Any ideas or heads up ? ((Keeping in mind I'm only 15 and aren't the most intelligent being on earth))