When you totally gut a bathroom to install a new shower stall and flooring, before you install a new shower stall the floor should be level. What happens if the floor is not level and the shower stall is installed? What can be done to remedy the situation?

There are several ways to correct it...

But first: you are not telling us how uneven the floor is. Is it sloping one way ? Or is it simply that the concrete is floated too rough ? Also, what type of flooring are you planning to install ? Can you post a photo of the shower area ?

Will this be a custom tile or a manufactured base and enclosure? Let me know, Tom