You have to work backward from the load and its primary
power, then to topology, your efficiency goals and so on.
This will lead you a component selection (FET, magnetics,
catch diode or sync diode, etc.).
Then you can figure out what it takes to drive those
devices. A 10mA uC pin is not up to the task, unless
you like a few microseconds of risetime and roasting
the power FET (switching losses will be heinous).
When you know your FET size, the available local gate
drive supply (which may or may not be the primary
input supply) and the logic voltage, you can pick from
the many options one that bridges the gap.