An overlay roof occurs when keep your existing roof as is choosing instead to shingle on top of it.
Overlay shingles roof.
They also last longer and stand up to foul weather better than shingles.
When you overlay a new roof you attach the new shingles or other roofing material to the existing roofing material.
Metal roofs offer energy savings but do cost more upfront than traditional asphalt shingles.
In general overlaying a new roof takes less time less labor and thus less money.
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.
That said overlaying asphalt shingles with a metal roof could be an option provided there is no underlying damage.