Does SQL Developer have any options to create a schema build script? Toad allows you to select objects (tables, views, packages etc etc), and I think now is clever enough to create these in the appropriate order, so generally constraint errors don't occur. I know you can export DDL to file, but couldn't find an option to build a script?
You drag your objects into the Cart and then use the Deploy button. It will generate a series of scripts. They are designed to account for creation order and to preserve your data if you want to include it.
Here's a quick overview of it
If you want the entire Schema, try the Tools > Database Export.