Building your own coaster is the best way to let your imagination go wild! When you complete the collection of cards needed for a coaster type, you can start building it.
To do so, check the Build menu, and drag the Custom coaster card into your park, then enter the Edit mode. Trace the desired track by dragging the first node of your coaster wherever you want, eventually looping to the end back at the station. Once the track is traced, you can select each node individually to modify position, height, or angle, and even delete it, or add a Special Insert.
The length of the track is limited by the Base Set card level. Upgrade that card to make a longer coaster.