Hello. I live in an apartment and an existing shower cabin in the bathroom is old and piping seems to become unreliable. So instead of buying a new one, I decided that the best idea would be to remove old cabin entirely and build a new one out of concrete and then add shower walls and then lay tiles. That way I'll get more space in the bathroom and also get the chance to hide drainage and water supply pipes. However before starting to work on this project I need some tips. In the bathroom, there already is a tile floor installed.

1. Should i remove tile floor before applying concrete to form base of the shower?

2. If i don't remove tiles, should i apply water resistant material on?

Thanks in advance.