Structural engineers... I'm going to build a shooting hut, need some help with design

[joem1945]

6" off ground will let critters and pests build dens under it. Raise it up some or you'll have some unwanted guests living under there.

 

[medalguy]

^^ This is what I was going to mention. I built a 6 x 6 foot shed much like your original design in New Mexico. I built it 4 inches off the ground and discovered pretty quickly that rabbits liked to burrow under there. One day I was shooting and a 5 foot Western Diamondback crawled out the front of the floor.

I would go the gravel route on the ground. If you really want to build it up, I'd go at least 18 inches so you can easily see under there.