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The cost will depend on which part of the world the work is to be undertaken. And since you have not bothered to share that crucial bit of information, I cannot provide a more useful answer.
Depending on your location, if the metal roof is going to be more durable and sturdier than your existing roof, you will need a permit. Also if the metal roof is going to heavier than your existing roof, it will require a permit.
In many jurisdictions, if caught, you must purchase a permit at twice its normal cost.
They may consider these things: Square footage area of the part of the roof that is to be repaired ; the pitch of the roof ; ease of access to the area ; the roofing material types that is to be used ; height of the building (number of floors) ; roof permit from concerned authorities of the state ; city license ; labor costs.
You're kidding I hope. Price varies quite a bit depending on where you are and the type of roof you have. One or two story, how steep, how many peaks, but that seems way out of line. 40 year shingles are probably around $100 a square, maybe $125. Single layer tear off should be half of installation and reshingle used to be about the same as the shingles to maybe one and half the shingles. If there is only one layer on the roof now, there is really no reason to tear off what is there. For that kind of money, I would get several bids.
Underground mining is very expensive, and "room and pillar" methods only permit removal of a portion of what is being mined- something had to hold up the roof.
Fire
I have a permit to drive this car. I'm about to get my permit.
Please permit me to answer this for you. You'll need a permit for that! My hunting permit expired last month.
Driving permit? Gun permit? Building permit?
roof scoop or sun roof
Your permit to do what, and where?