No one here is able to see what your working with, know what the price of labor and concrete and materials is in your area so anyone would have to just guess which will do you no good.
If this slab is to go up againt the side of the house then all the siding on the lower part of the wall is going to have to come off, Storm and Ice shield added, do the pore Install 1 X 6" vinyl lumber with Z moulding on top of thet then reinstall the siding. If you just pore up againt the siding the side of the house will rot out. Also the slab must be at least 4" below any door opening. If not water will get in a take out your subflooring.
Many times we had had to go back at replace rim joist, bottom plates in walls, floors, even foundation plates because someone did not water proof the wall first.