From Astro Wars
Note: if your food output is 0 you will need to increase the Population Limit via Social Science. In this way Population is unique, as it is the only level based value which has a maximum level (though as stated, this maximum can be increased).
- If "N/A" appears in the text value for remaining beside one of your buildings, this does not mean you cannot upgrade it further - the system is simply telling you it is more than likely cheaper to upgrade with Supply Units (SU) as opposed to Production Points (PP)
- You can never upgrade a Starbase with an SU and as such you will never get "N/A" appearing for a Starbase.