Riding high

How do they build roller coasters* and what do they build them of/from? We have been watching the new roller coaster being constructed at SeaWorld on the Gold Coast and it seems to be being made of wood ... but it could just be that that is the framework for holding up the real roller coaster as it is being built.  I know there are renowned wooden roller coasters around the world but I would have thought that metal roller coaster would be more cost efficient to erect these days.  We will just have to keep an eye on it to see what happens as it gets nearer to completion.  

*Oxford Dictionary: a fairground attraction that consists of a light railway track which has many tight turns and steep slopes on which people ride in small, fast open carriages.