We have just stripped out our old exisiting bath suite. (All was leaking).
We are rearranging the location of bath, sink and loo to accomodate new
suite.

The bathroom is quite small, and to be able to hide soil, waste and copper
pipes the walls would need to be built out.

If we raised the floor by 20cms this would hide all pipes.
(The existing floor is joists and floorboards. The old bath suite had a
cast iron bath, so can take weight.)

How do we do this?