Russian tortoise?????

okay, here it goes. i am interested in getting one. i would keep it in my backyard. on my back wall, there are bricks about a foot from the wall all the way down on both sides, but about four feet from each side, it curves out like this out on both sides about four feet out. i can't really describe it. yah... there is dirt all in it, the whole thing, would it be okay if i left the dirt in there and just took out the rocks so they could burrow in it? we used to have bunnies and they burried back there just fine. i only want to use the section of 4x4 for it. could i do that? what could i make the walls of so he wouldn't escape? i need step by step here. also, what would i feed them. exactly what kind of substrate do i need if i take all the dirt out? and what would i do for it in the winter?