I was looking around on the internet today and found this site. This site is where people have made different models of coasters out of the K'nex Screamin Serpent Coaster set. Some of the models are accully quite good. I have the K'nex set and made many models but I only have one set so my options are limited.
Anyways heres the site:
http://www.freewebs.com/rollerdudetw/knexmodels.htm