Hammocks can be made with clips attached or only tabs for detachable clips. Metal clips can chip the enamel inside a washer or dryer. I find I need several, one is always in the wash.
For these projects I used
Polyester fleece stadium blankets from the thrift store for $2.00 each
Polypropylene webbing from a belt strap cut into 4" pieces.
and 4 swivel clips from an old purse (they don't HAVE to match)
cheap shower curtain hooks
Step 1: Make a template or paper pattern
Or you draw something freehand.
Or cut a template from cardboard, this is best for rectangular ones.
Keep reusing the cardboard template to trace new ones.
For this particular design I made half the pattern, so that I can cut the material folded.
These are both 15 inches long by 13 inches wide, though they can be made wider or even smaller to fit smaller cages. I find with this size i can actually get TWO into one cage on different levels.
If you are making the 'sling' style, be sure to make the corners taper to no less than 4 inches wide to allow for webbing AND the turn.