New room, floor not level

[Davidmit]

Hi guys, my first post so go easy.

I'm currently renovating our very tired 1947 home. We've just had the brick wall and a chimney taken out from our bathroom. I am building a stud wall and intend to board and tile it.

My question is mainly about the ceiling and floor. I have made the wall square, however using my laser level showed one end of the wall is 5cm higher than the other.

This is because the floor although flat is not level.

Now I had intended to lay electric underfloor heating and self levelling compound before tiling.

Not wanting to make work for myself. Think I can can level to ceiling to the floor or should I start over and level the floor first. If so can somebody tell me how to level a plywood floor?? Thanks

Dave

[welsh brickie]

take up the plywood to the bare joists then screw 20mm thick battens on top of the joists and pack level then lay new floor on top.