I have to model the exterior and interior of the captain's quarters for this type of ship and can't find a clear schematic. Some of them have the captain's quarters in the very back on the uppermost level and other have them towards the front on the lower level.
Regardless of navy, the captain's quarters on a ship-of-the-line was always the highest cabin at the stern of the ship. Entrance to the captains cabin would be from the quarterdeck. Depending on the decade the ship was built in, the cabin would also include a balcony. Hope this helps!