i took over a planet from a minor civilization and then found out that they had built every single building available. I was losing a lot of money through that place. Is there any way to destroy buildings??????
Yes. Open up the planet view and press the "Detail" button at the lower left part of the screen. You will see a list of completed projects. By marking one of the projects, you will see project details and be able to Cancel it, which in reality means destroy.
Found that out quite by accident. The manual really needs some work.