I used 2" X 4" (white fir, WF) framing lumber. A 5 ft. deck, the purchased 2" X 4" were 10' length, cut two pieces. Most, home grade framing is spruce, which tends to warp/twist. Any A/C plywood works for a deck, A grade side up. I used MDO board, probably more expensive than needed.
Have fun with your nails and screws. But then I'm known to have a foggy head from time to time. Mike CT.