This is hard to explain not knowing what kind of porch you have. Assuming you have a raised porch, you will need a footing, concrete or block wall, and floor with remesh inside. Rebar attached to old porch, fill sand compacted, etc.
Build your forms with CDX plywood and braced up good with 2 bys. Form the overhang with a 2 by. Stake and brace solidly. Good luck.