I've done a ton of settlement building... even bypassed the object limit for two of them to keep building, and still haven't come close to running out of wood. Of course, I do scrap a lot of stuff at every new settlement I get. Copper was been my main limiting factor for a while, but I've learned to just tag what I need and buy it all out at my tier 3 general merchant and Carla every time I return to Sanctuary (my main town). I no longer have material shortages at all. I'm pretty sure even with my intense building, I won't run out of wood anytime soon... I expect I'll grow bored of the game before then. I'm already 70-80 hours with three huge settlements construction. I guess it helps that I favor steel over wood (less holes).
I suppose if you obsessively fully develop every settlement, you'll run out of wood eventually. At that point, it might serve you to dedicate one settlement as the 'general goods dealer town' and have 10+ tier 3 general merchants (everyone that isn't farming). Visit them once a day and buy out all the wood stuff and whatever else you need. Similarly, make a scavenger table town and see what they come up with.
I kinda like the idea of making a town full of scavengers situated inside the city... too bad food resource can't be linked between towns. It would be neat to let some of the farm settlements pick up the slack for more specialized settlements. Hopefully mods give us miners, smelters, scientists, chemists, and all kinds of other cool roles as well.