small pole barn advice

you can use material you have or bring in more material.
you want it to be pretty close to flat , with a little slope toward the front.
Am I reading your post right ?
You want to use 8x8 posts ?
If that's the case you only need 6x6 green treated . Here in Washington they need to be buried 4 feet in the ground. Not sure where you are ?
I would definitely poor concrete for floor.
Best of luck with the shop !!