I'm pretty sure this game hasn't been done before, so let's get started.
The object of the game, as the name states, is to create your own Pokemon League. You must pick 8 gym leaders, 4 E4 members, and 2 champions [one league champion and one secret champion, such as Red (GSC) or Steven (E)].
But there are some rules, to make it interesting.
Characters must have held that position at some point in game, so no making Volkner the champion and such.
Characters may only be picked once.
Types may only be picked once, and for the sake of fairness, multi-type also falls under this rule.
You may add as much or as little detail as you want, such as gym order and teams. That part is up to you.
Misty - Water
Gym Battle: Psyduck Level 12, Staryu Level 14
Wattson - Elec.
Gym Battle: Magnemite Level 17, Mareep Level 16, Electrike Level 19
Koga - Poison
Gym Battle: Golbat Level 22, Grimer Level 24, Skorupi Level 22, Koffing Level 26
Sabrina - Psychic
Gym Battle: Mr. Mime Level 25, Kirlia Level 25, Espeon Level 28, Kadabra Level 31
Norman - Normal
Gym Battle: Vigoroth Level 35, Loudred Level 35, Linoone Level 37, Slaking Level 40
Pryce - Ice
Gym Battle: Dewgong Level 38, Sealeo Level 37, Lapras Level 39, Piloswine Level 43
Blaine - Fire
Gym Battle: Ninetails Level 42, Magmar Level 40, Rapidash Level 42, Arcanine Level 47
Giovanni - Ground
Gym Battle: Golem Level 45, Nidoqueen Level 47, Nidoking Level 50, Rhydon Level 50, Mewtwo (Armored) Level 55
Grimsley - Dark
Initial Battle: Liepard Level 54, Scrafty Level 53, Absol Level 54, Krookodile Level 55, Bisharp Level 57
Bruno - Fighting
Initial Battle: Hariyama Level 54, Hitmonchan Level 56, Hitmonlee Level 56, Onix Level 57, Machamp Level 59
Shauntal - Ghost
Initial Battle: Cofagrigus Level 57, Gengar Level 57, Drifblim Level 56, Golurk Level 59, Chandelure Level 61
Lance - Dragon
Initial Battle: Gyarados Level 60, Kingdra Level 58, Aerodactyl Level 62, Charizard Level 62, Dragonite Level 64
Steven - Steel
Initial Battle: Skarmory Level 62, Cradily Level 61, Armaldo Level 61, Claydol Level 60, Aggron Level 65, Metagross Level 67
Red - Multi-type
Battle: Pikachu Level 88, Lapras Level 80, Snorlax Level 82, Venusaur Level 84, Blastoise Level 84, Charizard Level 84
I think I like the order, but I may add in teams later on.