shower curb

[arthur]

I'm not sure I got waht you mean, maybe a raised shower platform/stall? If so, define a portion of the bath as a separate room and in its Room Specification Dialogue, in Structure Tab, in Floor (C) insert a positive number. Expect that the overall height gets lower.
Here's a project I pondered for a friend with an open and raised bathroom. I raised the floor by 15cm, so the overall bathroom height is now 2m55cm from 2m70cm that was before raising the floor.