District Seven

This District covers the most heavily-wooded areas of Panem, and as a result their economic focus has always been lumber. However, a forest can only take so much chopping, so for the past few decades they've been moving into construction and allowing the country's forests to recuperate. It turns out this was a good move- Panem needs a lot of rebuilding, and no one knows how to construct or fix a building better than these people.