Red deal is the old term for pine. Basically Scots pine. Redwood. Pinus sylvestris. Mostly from the baltic and Sweden.
Not white deal or fir the stuff scaff planks are made from. Although it is light and strong. Just not the best for working(I'm guessing guys are using hand tools.)
It's much maligned in modern joinery but it's use was practically universal in times past. I suggest its got a great mix of strength and weight and solidity and workability/paintabilty. Even the knots are softish. White deal is stronger weight for weight but works really badly. It doesn't finish well off the cutters it's hasn't got the durability of red(but it does like pressure treatment) and the knots are like glass.
I'm not suggesting don't go dumpster diving for a second I'm saying if somethings worth making the make it with something decent that's available in sizes you want.