Sorry, but we only have a visual builder for Slick-C, which we use to build dialogs in SlickEdit. Our focus has always been on manipulating the text files for programming. We did a visual builder for Java once, and it left much to be desired so we discontinued it.
We find that SlickEdit works well as a companion tool in environments that rely on visual builders. Use another tool to layout your GUI. Then use SlickEdit for the fastest editing of the code underneath.