Stuff to use to make a cool bed that cats will like
Cardboard boxes with a comfortable lining ought to work.
Cats will sleep in seemingly random locations. making them a bed is pointless. my advice: don't bother, but if you REALLY wanted to you should follow knotted8's advice.
A cardboard box and a blanket or sheet. Or if you want to get very creative, you could buy material and stuffing and sew your own plush cat bed.