Im not to familiar with flashbuilder i use flash develop.
I will check my folder structure and get back to you (note im not very good with starling builder)
I remember setting up a project and just doing whatever it took to get it working. I believe i have the folders starlingbuilder, and layouts in my src folder along with my main.as and game.as
One thing though,in the picture it shows import starlingbuilder, which should be import starlingbuilder.* for the whole folder. Or import starlingbuilder.yourclass; like your other classes are