If you are not
going to use a prefab shower floor... (great idea AMRICCA... I forget these are out there sometimes)... then you will need to plan on using a membrane to create the shower pan
... on concrete slab or on wood floor...same rules apply
. Here, even though on concrete slab if water backs up in shower (for any reason) water can seep out the threshold or any place where the horizontal meets the vertical... understand..
For example, grout lines crack.. water will find the crack and it will seep down and eventually it will seek out where horizontal meets vertical (water is very good at finding these spots...especially AFTER you finish the job!!
You will also need to plan on installing concrete board ON THE WALLS up to the ceiling (if tiling to ceiling) or to just a couple inches below where you plan the tile to end (then blueboard and plaster). You cannot install hardibacker as a shower pan if you use a membrane for pan.
... how will you secure it? Adhesive won't work here... screws through membrane won't work here... only a poured floor will work here.
Check out this link: How to Build a Shower Pan
It breaks down the steps to install a new custom shower (with pictures... ;) ). These are a lot of work to do correctly... why many hire professionals to do. If follow all steps though, not really hard. Big issues occur when people cut corners... they are almost always disapointed!
Let us know what you think... let us know if need more information... Sorry I do not have better news!. Mark PS...let some of the other remodelers onsite here chime in to confirm what I say...they will be along shortly