What you need power nailer or roofing hatchet tape measure roofing shovel or flat pry bar hammer drill carpenter s square straight cut tin snips utility knife chalkline broom.
Overlay shingles roof.
This has advantages and disadvantages and each of those should be weighed carefully.
That said overlaying asphalt shingles with a metal roof could be an option provided there is no underlying damage.
They also last longer and stand up to foul weather better than shingles.
Metal roofs offer energy savings but do cost more upfront than traditional asphalt shingles.
When you overlay a new roof you attach the new shingles or other roofing material to the existing roofing material.
In general overlaying a new roof takes less time less labor and thus less money.