Gathering 1000 resources for crafting is pretty straightforward, just cruise around Sanctuary or any other settlement you have unlocked scrapping everything that highlights in yellow with the Square button (trees, ruined houses, cards, etc), you will accumulate wood and steel fairly quickly this way.
To actually get the trophy to unlock, you may need to go to the workshop and transfer 1000 resources into your inventory. I had 1,214 wood which unlocked it for me, however combinations of resources totalling 1,000 should also work (e.g. 600 wood 400 steel).