I am really new. In buildings, up to level 10 and it asks if I want to destroy level 9 which shows a zero. Why?

majestica wrote:I am really new. In buildings, up to level 10 and it asks if I want to destroy level 9 which shows a zero. Why?

Each upgrade of a building takes up available space on that planet. Eventually, one might run into the issue of there being no space left. To keep people from accidentally filling up all the available space, thus making it impossible to construct other structures, you are able to downgrade your buildings to make more space available.