Hi I am rebuilding a tile shower (first time) and have a few questions, (I have read many posts but I am still a little unclear) I had to tear out the old shower due to leaking and mold. I plan to tile the new shower (I have tiled floors before but not a shower) and make it a little larger. First off, I plan to use a liner but I have seen some use tar paper on concrete before preslope of the floor, do I need to use tar paper first or a liner before I preslope the pan? Or do I put the liner on after I fix the preslope? Also I have used Greenrock on the walls not concrete board do I need to change that or is that ok? Next I have seen some use some rails on the preslope, (looks like it makses it easier) do I need these because I have not been able to find them. How can I ensure I keep the correct slope to the drain if I can't use those?

I appreciate any assistance that is offered.