Personally grass! It would be a beautiful field arena with a water fall!

This is what my grass gym would be (if the player has 8 badges!)

Sunflora, Jumpluff, Vileplume, Bellossom, Leafeon, Levanny. So many cuties! :)
These are also most of my favorite pokemon. (Off topic, but I also enjoy snorlax, sewaddle, seel, poliwhirl, starmie, and a few others)

What about you? I know @pokejungle would have a bug gym!

As predictable as it is... yes, I would probably have a Bug-type Pokémon Gym and try to live up to legends like Burgh and Bugsy. Although a much newer Gym Leader to the franchise, I also enjoy Katy(did).

I really liked both of Burgh's Gym designs, so I'd want to hire his interior designer (lol).

If I were to choose a different type for a Gym, I'd have to go with what is also predictable, Grass! Erika is one of my all-time favorite Gym Leaders.

I made a gym team almost a decade ago, back in 2016, and I stand by it for the most part. (The Zoroark & the Liepard wear little jester collars and that’s the image on the badge)

Trick Badge; Must have six badges to challenge

Order:

Murkrow "Matthew"

Super Luck

Lv. 45

Night shade, Foul play, Sucker punch, Tailwind

Sableye "Eris"

Keen Eye

Lv. 45

Shadow sneak, Zen Head butt, Aerial ace, Poison jab

Zoroark (as Liepard) "Reynard"

Illusion

Lv. 47

Dark Pulse, Flamethrower, Shadow ball, Nasty Plot

"Ready for this trick?"

Whimsicott (shiny) "Pan"

Prankster

Lv. 47

Energy ball, Psychic, Shadow ball, Giga drain

Liepard "Puck"

Limber

Lv. 49

Night slash, Shadow claw, Payback, Iron tail