Plank is the most expensive item for the new BH. In Malaysia, the most common wood use for plank is Red Meranti. The wood must be no smell and not easy to grow fungus. The Red Meranti wood can be divided into 2 groups; Dark Red Meranti and Light Red Meranti. Dark Red Meranti is darker, harder and more expensive. Btw, I am not wood expert. For more details should check with Sawmill owner.
1. What dimension - 6 inch width and 1 inch thick. If shorter than 6 inch, the fur might easily stick to the nest.
2. How many plank require for 20x70' shop lot (1-storey) - Depend on nesting box design. If you use 3x1 feet nesting box for all your BH, you need ~ 1700 feet. 1200 feet about 1 ton. So 1700 about 1.4 ton.
3. How much - Right now Dard Red Meranti around RM3300/ton and Light Red Meranti around RM2600/ton.