How to design a roller coaster in Polynomial Graphing?

I have to design a roller coaster with at least four equations of polynomials. I have the first equation as
y = 4x3 + 9x2 + 2x + 5
But I'm not sure how to add more to make it look like a roller coaster.
I only have down two equations and it looks like this:

http://25.media.tumblr.com/79766b3f378c80b61686f6bd9f8eb310/tumblr_mia5z907hD1rv3dpeo1_500.png

Can anyone help me figure out how to make the lines in the graph to look like a roller coaster?

Question

How to design a roller coaster in Polynomial Graphing?

I have to design a roller coaster with at least four equations of polynomials. I have the first equation as 
y = 4x3 + 9x2 + 2x + 5
But I'm not sure how to add more to make it look like a roller coaster. 
I only have down two equations and it looks like this:

http://25.media.tumblr.com/79766b3f378c80b61686f6bd9f8eb310/tumblr_mia5z907hD1rv3dpeo1_500.png

Can anyone help me figure out how to make the lines in the graph to look like a roller coaster?