In general overlaying a new roof takes less time less labor and thus less money.
Overlay shingles roof.
They also last longer and stand up to foul weather better than shingles.
However this can only be done once.
When you overlay a new roof you attach the new shingles or other roofing material to the existing roofing material.
That said overlaying asphalt shingles with a metal roof could be an option provided there is no underlying damage.
This has advantages and disadvantages and each of those should be weighed carefully.
It s good to know that you can only choose this option if your roof has not been overlaid previously.