Because double berths are not much larger than single beds, is quite simple to use single adult bunk beds planes and re size using plans for a bed twin or double. The first option is a direct construction project; but the second requires further elaboration. The key is to build two heads and two foot bed that can be used in all combinations. The easiest way to accomplish this is to use commercial hardware to connect the bars with spare tips.
You will also need to focus and drill 1.25 cm. Then you assemble the lower bunk using both headers and the upper berth using both feet in bed; insert 1.25 cm diameter holes in these beds remain in place. Strong corner posts are important for all beds, but especially to raise the adult bunk beds. While not much higher than the single, double should never use anything less than 4 x 4 or 2 x 6.
The mattress supports should also be thicker for double adult bunk beds. You can use 2 x 4 to the slats of the bed. Sidebars should be at least 2 x 6 with 2 x 2 glued and screwed into the bars to hold them, but rotate them so that one side of 5 cm faces up to provide greater strength.