Doll beds are easy to build in sizes for most dolls houses, or you can adapt these instructions to make a custom sized bed for any size of doll. In 1:48 scale, the bed is easiest to build from card, and for 1:24 and 1:48 scale you will find it easier to use flat butt joins instead of mortise and tenon joins.
The mortise and tenon joins shown in the instructions give the bed more stability, and make a stronger piece of furniture, especially important if the bed is for a child's play. They are fairly simple to cut, and are a good technique to learn for fitting sections of wood together where the resulting join will have weight placed on it.
The bed shown in these instructions was made in a standard single size. Beds have only recently begun to come in in standard sizes. It was common until the last fifty years to have beds which were various lengths to suit their owners. If space is at a premium in your dolls house, you may want to adjust the length of the bed to a smaller size to fit a room. Building the bed with a bottom rail instead of a footboard is another option. To do this, you join the bottom rail to the legs with a mortise and tenon joint, just like you join the head and footboard to the side rails in this set of instructions.
To build a bed for a larger doll, use appropriate thicknesses of wood for the size of the doll, and build the bed to fit the particular doll, leaving extra length for pillows and bedding.