There is no special requirements for an ordinary inside SWL antenna. A piece of insulated wire anywhere between 10-25 feet long will do fine. Drape it over the curtain rods, pin it to the ceiling around the perimeter of the room, hang it vertically in a stair well, whatever. You will likely have less man made electrical interference if it is mounted horizontally, but experiment.
If it's silly and it works, it's not silly".