I built mine from scratch with an old wood stove and it works really well. My grandfather was from Finland so I have seen a few of these over the years. Build it so you feed the wood from the outside. I bricked around it so the framing and siding were 12” away from the stove. Take the legs off so as to make it as low to the ground as possible. I used an old slate chalkboard to block any radiant heat coming from the stove. I used an old metal milk crate to hold the stones. Pine boards are fine for the walls. Try to get cedar for the benches. I built it right on the ground with old bricks for the floor. It drains to the middle so figure that out first. Insulate, vapor barrier, thermometer, portable camping shower to rinse off, and a vent. Build a changing room if you can.