make down a bed—prepare sleeping accommodation not previously available (when one has a visitor, etc.):
- Are you going to sleep here tonight; if you are, my wife will make down a bed for you.
make up a bed— = make down a bed:
- She made him up a bed on the high white divan in her living-room—not a heap of sleeping-bags and blankets but a real bed.
See also: make a bed / make one’s bed.