Increase the silo/barn storage by going into the silo and tapping on the "increase storage" button. With enough nails, screws, wood panels, you can tap the check button and your silo will be upgraded right away. You can get upgrade items from crops and animals. You can buy them with diamonds.
Also, at level 14 you will be available a map of the world. Sending goods to open cities and you get resources to improve the barn and warehouse.
Advice: If you want to increase the chance of upgrade items plant more wheat. It grows every two minutes so you have better chance to receive desired items.