You can make "gutters" or rain channels in a variety of ways. If you want to use flashing, get someone to bend the coil stock into a shape something like this it will minimize large debris from entering your water trough. Sure, you could add screening, but a flushing system before the collection pint
should keep everything pretty clean. Basically you are making something close to a gutter helmet system.
Or, you can cut a part of the arc out of pvc pipe and secure that tube to your roof edge. When you get to the end you can either use rain chains or more pvc.
It is difficult to gather roof rainwater without something there, and you want to keep water from pummeling your foundation area, anyway.