Here are some steps and tips to making the perfect Pokmon Gym ^_^.
I - Being a Good Leader:
A Good Leader will always know what to do in his or her own Pokmon Gym. Try to come up with a humble attitude, coming up with good teams, and following all the rules--including your own!
II - Your Gym, Inside and Out:
The outside of your personal Gym will look like is most likely already decided. But the Inside, isn't, you're left to do all the work on the Inside. Try to come up with something that respects the nature of your gym, as well as something your pokmon's elements will respond to! You wouldn't want to have a lava-filled gym when your training Grass-Types.
III - Levels, Pokmon, and Elements!
A Key Factor, your Pokmon, the levels, and the elements! If you have an official gym, your going to have to remember that you can't have an "any-type" Gym. You'll have to pick one Element, Even if the Pokmon are different Elements. Onix and Marowak are both Ground-Elemental Pokmon, even though Onix is part Rock. Now about the levels, You do not need ridiculous leveled Pokmon!
Using These ideas, I'm going to Show my Gym ^_^
Leader: Dizzy, Master of the Flames
Element of Gym:

Pokmon Line-Up:

Level 44,

Level 43,

Level 43.