Here you see the cabin facade standing in place on the support you glued to your shelf, the porch support pieces lined up in place for the porch to attach to, and the porch floor sitting in front, not yet attached. The porch support pieces run from one corner of the house, across the front of the shelf (set 5/8 inch or more back from the shelf front, this will depend on how far forward you glue your facade support in the previous step)
Lay out your pieces to determine where they will fit on your shelf, with the porch support pieces lined up to fit flush with the outside edges of the porch when it is against the house. Do not glue the porch supports in place until you have the facade mounted to the support (several steps on).