Answer:
Big as a saucepan, deep as a cup, Even a river can't fill it up. What is it
They come in many varieties: Red, Black, Dead, and Caspian to name a few.
It is something you make after you've weighed your options.
You fill it and it empties, A metaphor for plenty, Depending on what half you see, It's either full or empty
It's what light turns into in the night
I am a room that has a roof but no walls. What am I?