When I was 12, my dad reclaimed the wood floors from the local synagogue that was being torn down. All told, he probably laid down close to 1600 sq ft after we spent quite a while removing nails, sorting the wood, etc. The wood was tongue and groove and he nailed it to a plywood subfloor. The last row of flooring was face nailed but you can't see it unless you start looking.

Nice results for a little cash and a lot of sweat.