Layout and structure
Personally I like to be able to see the whole canvas so if it would be possible to have a zoom option (if there isn't already)
When the builder is up at first I was overwhelmed by loads of options but as I studied it a bit more I managed to figure it all out so I was wondering if it where possible for those who are not educated in the layout a step by step introduction to the layout and where every thing is.
Another idea would be like PS where there is a way to arrange the options to the users preferable layout.
Last but not least a layer system so it is easier to edit each layer added rather than have a build up of shapes which if one was behind the other it wouldn't be needed to be moved in order for it to be accessed.
Over very nice concept and I really like the idea of it being completely customisable