Using private fencing boards i would like make a Harringbone flooring for my living room.
perfect video to watch https://www.youtube.com/watch?v=AQrRvyTcItk
Are the fence boards new or old? If they're old, you'll have a lot of prep work. They're probably weather, splintered and splitting. How wide are the boards, the wider the boards are the bigger the chance of cupping.
You really should use hard wood. You'll waste all your time because old fencing wood will not sand smooth, will splinter and not hold a good finish.