How do I enter/exit structures?

I can’t go into the structures I make without teleporting on top. I can make the roof intangible, but I want to be able to go on top of the buildings as well as inside them.

Your character controller has a step offset that is greater than the roof height. This means that it thinks your roof is a staircase, so therefore it tries to walk onto it. Lower the step offset in the inspector for your player’s character controller component.