*At a Mt. Olympus meeting, a half-blood child of Athena (brain child, read Percy Jackson...) discovers she has a hidden talent to make olive trees grow
*Medusa is just playin' around one day when she decides she hasn't done her hair lately. How in the world do you groom snakes?
*Apollo is bored (oh no) and decides to k=make a new instrument. The, "________". Poseidon is helping him and insists it be water based. Then Zeus is like, "I wanna help!" so lightning is always thrashing about inside. Hades, of course, gets jealous and declares that you play it with bones. Athena makes up music for it that is written in mathematical equations and Hermes insures free shipping. Hephaestus makes all the gears work and then Aphrodite makes it has a lovely sound and appear attractive to play. Persephone dots it with flowers and Artemis makes it shine with moon-light. Demeter fills it with wheat (they still don't know why) Ares declares it will sound every battle cry and Hera proclaims that it will bring joy to every home. Hestia fills it to bring warmth to every heart.
Making one up? I had to do something similar for a history project. So think of something in the world. For my project I did a volcano. You can do a waterfall, a desert, or anything else. Then take your favorite god/goddess and just think of a way to incorporate them creating it. Best of luck!
Make a god or goddess of dreams. One who do not honor will sleep forever in nightmares and ones who follow will have dreams come true. You could have sleep walkers. Conflict with other gods causing their offspring to never sleep.