When your restaurant gets bigger you will need to expand your storage too. 

This is because you will need more ingredients and more space to store dishes you have cooked. 
When playing the game you will collect tools, these you earn from clients as tips and wholesale deliveries. 

You will need a certain amount of tools each time you upgrade your storage rooms. 

This is easy to check! Follow the below steps: 
- Press on the storage room you want to upgrade. 
- Press on upgrade. 
- Here you will be shown what tools you need, and how many you have already to upgrade. 
- If you have the required amount of tools then simply press on expand. Simple. 
- If you do not have the required amount of tools, you can either wait until you collect them from playing the game, or buy them with Gems.