Inspect the joints between the sheets of metal roofing before you begin. Determine which sheet is on top at the point where two sheets overlap, and begin removing them on the side of the roof that has the top sheet.
Remove the screws or nails that hold the sheets of roofing to the sheathing underneath them. You can pry out with a crowbar. If screws are holding the roofing on, you can remove them with either a drill set to reverse or a crowbar; which is easier depends on the type of screws and the condition of the roof underneath them.
Take care not to damage the metal roofing if it is in good condition. Metal roofing is expensive, and undamaged pieces can be used elsewhere and save you a lot of money.
Lift a sheet of metal off the surface of the roof after you have removed all the nails or screws holding it down. Lower the metal to the ground, or throw it down if it's in poor condition and being discarded.
Remove shingles in the opposite order that you install them. Begin at the top of the roof by removing the shingles from the peak.
Remove the peak shingles and the uppermost row or two of shingles by sliding the claw of a claw hammer underneath them and prying them up. Remove all the nails from the roof sheathing.
Use a shovel or a shingle remover to remove large sheets of shingles when you have cleared a space large enough to use these tools effectively. A shingle remover looks a lot like a shovel, but has notches cut into its end that help it to catch nail heads when you pry upwards on shingles.
Throw all the removed shingles into a single pile on the ground rather than letting them fall everywhere. This will make them easier to clean up.