This will be a series from Alien / LoneWolf7 (Alien wrote it, LoneWolf7 posted it), where he step-by-step, teaches us all how to properly design & import, as well as including many tips and tricks for the upcoming custom scenery authors. There are a few requirements to following this tutorial. For starters, you need Google’s Sketchup, and a few plugins for the creation. These are free of charge, and the plugins have been compiled into a ZIP for easier access (rather than scourging the ‘net for them).
available on filefront
You may also want to consider downloading the latest importer for RCT3, seeing as you won’t get your creation in any other way without it.
There’s plenty of screenshots included in the post for all you visual learners. It is a great resource for all those confusing buttons on the importer, as well as sketchup. So if you want to push your limits, try this out, and get an object or two into the game.
View the tutorial here: http://ataricommunity.com/forums/showthread.php?t=668369