Advice please!

New build, family bathroom design question. See image for current layout, space is 3385 x 1600 mm. What is involved in moving the toilet next to the sink, and pivoting the bath 90 degrees, to run along the external wall? The builder is providing the units but yet to be installed. The pipes for the shower unit have been located over the tap area of the bath.

Do I need a builder to first confirm if how to joists run, to see if the waste pipe can be extended? Anything else i need to consider? Also would appreciate any tips re storage within the space (closed door storage).