Honestly, you won't need anything to create enough of a slope to get the sort of drainage you want. Just work outwards (from the point of drainage), and use a level to make sure it drains inwards. Apply a little more adhesive as the tiles work outwards to create the drainage inwards, and just use a level at the end to make sure the whole thing drains inwards. Look up how to tile a shower in google and you'll get quite a lot of good information!