TMC wrote:

Do you really mean 2 inches drop per metre of floor as this would equate to
8 inches of height difference across a 4 metre wide room. I assume that you
have no door opening on the side that you have to lift by this much.

What is the actual height difference across the whole room?

Are the walls out of vertical as well?

Tony

It is a fair old drop, but it isn't consistent across the whole room.
Basically. there's a dip in the first metre from the doorframe that is
probably just over an inch. There's then a much more gradual slope
across the whole room. I really should measure it up properly to
establish the severity of the slope.

The walls are surprisingly ok.