Well, I had a fan fiction where I had to come up with ten gym leaders and rosters for a region I made myself, but rather than bore you with 10 different gym leaders in cities you probably won't have any idea about, I'll just do what I envision my home-bred character would do if she was a Gym Leader.
Name: Lisa
City: Fort Mill, South Carolina Sunyshore City
Number: 8/Final
Type: Mixed-type Gym.
Pokemon and Level:
Persian, Lv59 (Fake Out, Bite, Aerial Ace, Return)
Metagross, Lv58 (Meteor Mash, Earthquake, Ice Punch, Agility)
Jolteon, Lv58 (Thunderbolt, Shadow Ball, Hidden Power, Thunder Wave)
Flygon, Lv57 (Earthquake, Outrage, Roost, Fire Punch)
Walrein, Lv57 (Ice Beam, Surf, Hail, Substitute)
Weezing, Lv57 (Sludge Bomb, Flamethrower, Thunderbolt, Shadow Ball)
Badge and TM: Century Badge, and player's choice of TM13, TM24, or TM35.
Gym Layout: Long straight hallway with many fancy decorations. Gym puzzle is a series of trivia questions on a variety of subjects including "Algebra", "Chemistry", "Full Size American Automobiles", "The Hospitality Industry", "Major Fraud Cases", and "South Carolina Highways."
Anything Else you want to add:
Picnicker, Lass, and Parasol Lady are subordinate trainers.
Nickname (on statue outside Gym) The Calculus Queen
Dialogue:
Before Battle: Please, allow me the opportunity to welcome you to this most impressive facility. My name is Lisa, and I am the leader here. By making it to my chamber, you have proven yourself worthy of a battle with me, the region's highest-ranked Gym Leader. I must warn you, do not be lulled into a false sense of complacency because of my frilly dress or my calm demeanor. Many trainers before you have made that error in judgment. Well, I trust that you are ready to commence battle. Let us begin.
Mid-battle: Not bad. Like myself, I can see that you have carefully planned your battle strategy.
On the ropes: Things are not going as I had calculated... Still, do not count me out yet!
Loss: No! I definitely did not anticipate this outcome! Your strategy has thoroughly bested mine...
After: I see. As you have made it this far, perhaps it should come as no surprise that you were able to defeat me. But I quite enjoyed our battle. You have proven that you are worthy of being awarded the prestigious Century Badge. On your way out, please speak to the receptionist for your TM. Now, with eight badges in hand, the Pokemon League is your next destination. The League is not to be taken lightly, but from what I have seen of your skills, you should be able to hold your own against our esteemed Elite Four. Go forth, and show them a battle as intense as ours was.
Rematch: All Pokemon are Lv85-90.