Keith Yousef

I helped a friend with something similar, and the first thing we learned was not to put the insert straight onto plywood. We built a proper hearth with cement board and tile, then raised the insert on a solid non-combustible base. It's worth checking the clearance requirements for your insert before deciding how high it needs to sit.

For the roof, we used a metal roof flashing and a high-temp silicone boot around the chimney pipe. It's made for metal roofs and has stayed completely watertight.

That looks like a fun project. I'd spend most of my time getting the firebox and airflow right first, because everything else depends on that. A good draft will make it burn hotter, cleaner, and with far less smoke. If you're using reclaimed materials, I'd definitely use firebricks around the burn chamber, as standard concrete or paving slabs don't usually cope well with constant high heat.

I used porcelain tiles under my wood-burning stove, and they've been an excellent choice. They cope with the heat without any issues, protect the floor from sparks and embers, and are really easy to clean when ash gets around. Just make sure the hearth is built to your stove manufacturer's clearance requirements and local building regulations. It's a practical, durable solution that also looks great.