I have seen some remodelling done where the standard bathtub with tile surround was ripped out and replaced with just one big 60" shower. The questions I have may be stupid...but then again maybe not. After I pull out the tub, via sawzall or whatever means, i'm assuming I would then rough use 3/4 plywood, with 1/2" concrete board ontop of that ? This would give me the floor of the shower..(would need to slope to drain), but then how would I build the lip/side/step (right terminology escapes me) the you step over to get into the shower..simple framing with concrete board to handle the tile ? For the sides I would simple ripout the old tile and replace with concrete board/new tile.