How to upgrade my storage?

There are several resources in Zero City that can be stored. Each has its own room for production and another for storage. The production rooms offer a little storage themselves.

Money is produced in the printing room and then stored in the Vault, Food is produced in the dining hall and stored in the refrigerator room etc.

To increase your storage of each resource build or upgrade the relevant rooms. You can check in the Market option under the production tab for the rooms that you can build and what they make or store.