Hey,
I was working on a roller coaster last year and finished most of the ride. Since I somehow lost interest in it, I decided to show you the progress so far before I dismantle everything.
I'd like to point out that I cut some coaster track pieces for this MOC, see here! Poor LEGO pieces, I hope you can enjoy the coaster nevertheless.
The whole coaster is built on two 48x48 baseplates. The coaster is 76 bricks high. To cramp everything onto two baseplates, I used a very steep ramp using customised pieces.
Click for a VIDEO
For the dive, I used two curved pieces as proposed by others.
The big looping consists of unmodified lower ramp pieces, while the steep curve was built of modified ramp pieces (see above):
The white platform was decorated with some shiny pieces by my 5-year-old daughter. ^^
For the two smaller loops, I used standard curves, a technique similar to the dive section depicted previously.
The chains used for the ramp had to be diverted to work. Still, the chains do not run as smoothly as desirable but most of the time they are doing their job.
For the upper part of the ramp, I again used modified parts. Obviously, I did not achieve optimum results but it works.
Also, I'd like to share a 100% legal version of the double looping which was not depicted in the previous pictures. It reminds me of the large hadron collider:
You can find more photos in the flickr album.
I hope you enjoyed it.