The Sawmill allows up to three Dragons to collect Wood. There are three Sawmills available to be constructed and upgraded, one on Berk, one on Old Forest and one on Dragons Cliff. 

The Fish Hut allows up to three Dragons to collect Fish. There are three Fish Huts available to be constructed and upgraded, one on Berk, one on Old Forest and one on Dragons Cliff. 

The Smithy allows an unlimited amount of Dragons to collect Iron. Completing the Fading Memories quest or directly building the Smithy unlocks Iron.