You can install a metal roof on any shed roof fairly easily, except a barn style gambrel roof with overhang. This is because the overhang has a negative angle and needs careful flashing to prevent that joint from leaking. But it can still be done as demonstrated in these photos.
The dis advantage of a metal roof is that it is more expensive than shingles, and requires additional planning and tools. Often times metal isn’t readily available and you will have to special order it and wait. Otherwise metal is the best roof option.
Roofing metal comes in standard lengths so you might have to cut them to fit. You can do this with your skill saw and a metal cutting blade.
Then you will need some flashing at the top of a gable roof. For a barn style gambrel roof you will need flashing at the top and the 2 middle points where the roof slopes meet.
Find out how wide each piece of metal is, then divide the width of the roof by that number. You will need this many pieces for a single sloped roof, or each of the 2 slopes of a gable roof, or 4 slopes of a barn style gambrel roof. You might have to stagger the metal and cut one or both outside edges to get the correct overall width. Then trim all edges of the roof with metal trim made for that purpose.
Build the roof as normal with the trim, felt paper and metal flashing. Then attach the metal roof material with screws make for roofing. They will have a built in drill bit and a rubber washer at the top. Ask your supplier how to use them. But typically you will drill them through the tall ridge of the metal until the washer comes into contact with the tin. This washer will seal the screw against the metal.
Then put the flashing on at the top, and on the sides where the 2 roof slopes meet for a barn style gambrel roof.
If you have to cut the metal to the correct length then put the cut edges under the flashing and leave the factory edges at the bottoms where they will be exposed.