Your best bet is to make a scenario with all coasters, all scenery, maximum loans, and
save that. You can then place scenery and all that stuff and still have money. Save the
coaster the same way you do in the Builder tool.

First, you cannot use scenery in the ride builder. Second, in order to use scenery, you'll
have to go to a regular scenario (such as build your own six flags park) and build your
coaster. Add the scenery, and then simply head to the save disk after you test run it.
Click it, head down to Save Track with Scenery, and select all scenery you want with it.

Custom Coaster Building does not let you use scenery. Sorry!