I think I'll start us off with the basis for a region which is the map, basically this map can be left up to interpretation on the climate, since it is a large land-based region expect a lot of Pokemon from all types except the truly oceanic Water-types (Tentacool, Remoraid, Wingull).
So this can be a start I'll edit it further to include more detail but yeh...

- Gym Cities/Towns (Golden)
- Regular Cities/Towns (Red)
- Special Locations (Caves, Forests, Towers) (Blue)
- Land Route (Yellow)
- Sea Route (Cyan, Dotted)
Gyms (Gen VI)
1 - Big South-Western City - Rock -
Geodude Lv14,
Carbink Lv17
2 - Right-Angle North-Western City - Flying -
Tranquill Lv20,
Fletchinder Lv23
3 - Small Central-Western Town - Grass -
Sunflora Lv25,
Nuzleaf Lv24,
Trevenant Lv29
4 - Wide Central City - Bug -
Pinsir (E) Lv31,
Beedrill Lv33,
Vivillon Lv36
5 - Small Central-Eastern Town - Steel -
Steelix Lv38,
Aggron (E) Lv40,
Aegislash Lv41
6 - Big Central-Eastern City - Fire - Houn
doom (E) Lv45,
Magcargo Lv47,
Camerupt Lv46,
PyroarLv49
7 - Small North-Western City - Ice -
Abomasnow (E)Lv51,
Froslass Lv52,
Beartic Lv52,
Avalugg Lv55
8 - Wide South-Western City - Dark -
Spiritomb Lv58,
Tyranitar Lv59,
Sharpedo Lv59, Mala
mar Lv62
Elite Four and Champion
Pokemon League - Tall South-Western City - Any Order
A - Water -
Gyarados (E) Lv65,
Quagsire Lv65,
Vaporeon Lv66,
Wailord Lv67,
Clawitzer Lv70
B - Fairy -
Gardevoir (E) Lv65,
Togekiss Lv65,
Sylveon Lv66,
Whimsicott Lv67,
Florges Lv70
C - Psychic -
Alakazam (E) Lv65,
Gallade Lv65,
Espeon Lv66,
Claydol Lv67,
Delphox Lv70
D - Electric -
Manectric (E) Lv65,
Eelektross Lv65,
Jolteon Lv66,
Magnezone Lv67,
Heliolisk Lv70
Champion -
Garchomp (E) Lv75,
Ampharos (E) Lv76,
Charizard (E) Lv76,
Vanilluxe Lv77, FlygonLv77,
Dralgalge Lv80
(E) - Mega Evolves
Of course feel free to disagree and change gym leaders and Elite four that's just my opinion