Current plan is to skirt it with pressure treated wood, then install board and batten I have been sawing above that. Flooring in the forge area will be crushed pea gravel, I find its easiest on my feet. The main mechanic area will be larger stone until funds allow concrete. I am planning on pouring one corner 6'x10' with concrete so I can frame it in and insulate it. I'm going to keep my mill, and future lathe in there to keep it away from all the dirt,grime and condensation. Going to add a little wall stove and window ac unit to give me a lounging spot in all seasons
Here's is the mill setup I have been using. Nothing fancy but it makes boards.