Considering what the Sentai shows are like (and obviously Power Rangers since it's just Sentai with reshoots), it can be practically anything.
No seriously, it could be anything as long as these criteria are met:>3 or more main characters.>A henshin scene in which they get color coded spandex suits with odd motorcycle helmets.>Fighting an army of identical goons sent out by villains mostly sitting in their lair.>Monster of the week that turns giant, forcing the heroes to pilot a giant robot
Beyond these vaguely defined points, you have complete creative freedom.
Want to make the show about six alien warriors who get their powers from the Greek Gods and pilot robotic moose to fight mutant squirrelmen from the future? As long as you stick to the above criteria, go ahead!