People often ask for "queen sized", or even "kingsize" bunks, basically bunks as wide as the double bed in your house. However a bunk that wide is often not feasible, or even desirable, on a boat. For one thing most bunks touch the hull on at least one side. That means you cannot fall out, unlike your bed at home. So the bunk can be narrower, yet still be comfortable. I've found that 1.1m, 3ft6in wide is about the minimum for a double while a 1.2m, 4ft width is comfortable.

Another point is that your bed at home doesn't move! If you sleep when passage-making you'll find you probably prefer a narrower bunk so that you don't roll around.

I prefer to sleep aft when at sea, as the motion and noise is less, even if I move to a forward bunk when at anchor. Indeed, if I am skipper on a boat I prefer to sleep in the saloon, so I can access the cockpit quickly. That's one reason for drawing straight sided saloon seats, and why I often draw the longest one wider than the others.

The jury's out as to whether its better to have bunks that run lengthways or ones that go across the boat. I've slept in both types, but some people find transverse bunks uncomfortable at sea, so I normally draw fore/aft bunks

Even on my smallest boats I always draw bunks with sitting headroom for at least the first third of the length. That means you can sit up in bed to read, or turn over easily or even do "adult stuff". Too many boats have "coffin berths", or bunks pushed under cockpit seats, so the "headroom" over at least half the bunk is more like "stomach room".

Apart from anything else, such bunks get very hot, even in temperate climates. Think about the real 3D space when you're looking at the drawings of a boat you plan to build. Of course it's best to go on a sistership to check it out, but I know that often isn't feasible.

And a final thought - how do you actually make a bed and tuck in a sheet if it's too low to get to the foot end?