Currently there is a feature where you can buy with Gems resources to add existing to deposits in the world, but I think there should be more flexibility for players with the two primary building materials in the world - lumber (wood) and minerals (stones).
Now I have less than 200 normal stone in my inventory, but over 6,000 pinewood planks. It would be great if players could offload these massive quantities of planks, in exchange for a percentage of stones in return...
This technique could also be applied to each material-tier; i.e., trade hardwood planks for marble, and exotic wood planks for granite.