Hope your ready for a wild-*&^ suggestion. Measure to determine where your blast furnace intersects the roof, and then cut your blast furnace at the same angle as the roof pitch. Use one side of your blast furnace to mark whatever you are using to make the corrugated roof (preferably before the corrugations are "modeled"), and remove the material to make your furnace hole. Then add your corrugations to the roofing material, slip the two pieces together (through the hole) to be sure they fit, and then glue together.
I would use material for the corrugated roof that is a good bit bigger than the intended roof size so that you can trim the roof to fit after you get the blast furnace (already glued into its hole) positioned properly.
Just a thought.
Chuck
