How do you build a rollercoaster out of paper?

You can start by rolling up varying sizes of strips of paper on toothpicks and chop sticks skewers, pencils, etc., into tubes. Glue or tape them shut, use them as girders. Use heavyweight copy paper if you can. It has more strength than notebook paper, but is more flexible than construction paper. The tape in long strips can be your track, with glue connecting the track to the major support features. Look up roller coasters or amusement parks online, and you will see how they are designed and supported.