The official Dusty Desert scenario guide suggests you build them in a certain order, though I don't know how helpful that actually is.

http://rct.wikia.com/wiki/Dusty_Desert/Scenario_Guide

General tips for increasing roller coaster excitement for any coaster type in any scenario:
- Build the coasters extremely close to each other, to the point where they intertwine.
- Place paths near the coasters. Let the queues pass over and under the track if possible.
- Build some portions of track underground. Even a tiny subterranean tunnel can make a noticeable difference.
- Build scenery as close as you can to the track. Use any scenery pieces for this except walls and fences; those don't affect ratings.
- Build water under the coaster.

Thank you for the info