could be a nice add to have a visual representation of the plate before slicing (with the possibility to import more than one stl and to rotate/move them for optimization of the print )
I use Slic3r (the newer 0.8.2 version has a much better plate builder), NetFabb or Repetier-Host to scale, rotate and create build plates, then re-export them as .stl and slice with SF. It would be nice if SF could do it, but sometimes it's better to use a program that specializes in it.
