sloping floor

Background: My mum has a wet room that is leaking. The wet room was installed in 2019 by a builder who claimed to be a plumber. The wet room is located on the second floor of a circa 1930s terrace house. Due to budget constraints, my mum opted to get the company to replace the floor and tiles...

I'm using self levelling compound to repair a crumbly old hearth (crumbling bits all removed), so that I can tile on top in Victorian style tiles. It's just a decorative hearth in a bedroom, so no actual fire. BUT, the floor is on a bit of a slope! What's the best way to get my hearth to match...