If one puts up the scach of the sukkah before building the walls then the sukkah is pasul (See Rama OC Siman 635 Sif 1.) If however a tefach of a wall is put up next to the scach (somach to the scach) before the scach is put up then the Rema says it's permitted to add the scach afterwards then finish off the walls. What about if the tefach of the wall was put at the bottom of where the sukkah would be. Do we say "gud asik" in this case and look at it as if the tefach is "somach" (next) to where the scach is?
The Dirshu Mishna Berura quotes R' Elyashiv ZT"L that even if the tefach is on the ground the Succah is kosher. (mishna Berura 635 s"k 11 #8)