What Corey did works great, however, for your size coop I would suggest adding two more blocks in the middle (one on each side) just for added stability.
There are two potential issues with what Corey did:
One is that rodents may think it's a great place to hide and live (underneath) so you will want to either raise it higher (so the chickens can get underneath and keep the mice away); keep it mowed completely clear all around and out a good eight to ten feet from the sides or; bury hardware cloth down in a 12 - 18" trench around the edges and staple it to the sides of the building.
And, two is that depending on where you live if your soils move at all your floor and/or walls could crack in the future from not having cement piers buried in the ground. That is a huge issue here in Colorado but in other areas of the country you never have to think about it. Just make sure you check if you have expansive soils where you live.
The very best floor, IMO, is a solid cement pad but that's more expensive than most of us can afford so we use a good, solid wood floor. I would also recommend covering the wood with lino to help make cleaning easier.
I'm so excited for you that you can have chickens! Hip, hip, horray!!
