Installing gutters on a metal roof can be complicated: if you do not use the proper screws the gutter will fail. If you connect your gutter directly to the metal roof you could damage your roof and your gutter might fall off during a snowstorm. There are various ways of installing gutters to a metal roof but the most practical and secure way is to use long metal gutter screws.
Measure and cut the gutters to the desired length you want. For seamless gutters you will have to hire someone to measure and cut them for you. It requires special equipment to make seamless gutters.
Install the gutter brackets on the fascia. Drill the gutter brackets to the fascia using your drill and the metal screws. Put a gutter bracket every 16 inches starting from the corner of the fascia where the gutter will be placed.
Lift the gutter and snap it into place in each of the gutter brackets.
Secure the gutter to the bracket by drilling in a sheet metal screw.
Hammer a spike and ferrule every 12 inches along the gutter. Hammer the spike through the tip of the gutter, insert the ferrule, or the sleeve-looking plastic piece, into the spike and then keep hammering in the spike until it's flush with the gutter.
Connect the downspout to the gutter using sheet metal screws.