I will triple that suggestion to build mock-ups. I did that to build a pilot house using pine 2x2's; 1.25" PVC pipe; and 1/8" plywood
for skin. Building each piece and assembling it with sheetrock screws. I could then back away from the boat and look at the angles and relationships of the various components, sawing away a little here or adding a little there to make the whole unit look good and function as to headroom
and other factors.
- - But for any cabin
design, I strongly suggest incorporating into the design access to sidewalls where plumbing
and other functional parts
of the boat are located. Don't put a settee so that you cannot get to a critical mechanical/electrical or other part for service
without totally removing the settee.