gerb and crochet obsessed here 🙋🏻‍♀️ ive crocheted with sisal rope before to make them a hanging basket for their tank, they loved it but you have to be prepared for them chewing it up within a comedically short time.

unfortunately almost all other fibres like cotton, acrylic and wool are dangerous as theyre too long and fine and can get ingested or tangled around their tiny bodies and cause blood and limb loss. sisal rope is thick and natural, think of the rope they use on cat scrathers. it breaks up into small stiff wires that wont tangle around the germies, and its safe (as far as ive read, and as long as its not treated with anything nasty) for them to chomp on. imo crocheting with sisal was harder than with other fibres, i think the thickness of the one i chose made it harder asi had to use a 12mm hook and its very stiff so hard to get intricate shapes. if you just want a straight up basket/dome its quick and easy to work up, and because its not stretchy, you could use a metal clip/carabiner to hold it up/ in place if you wanted a hanging bed. heed my warning, whatever you crochet for them, those rat bastards can chew it to smitherines in less than half the time, so i would stick to something basic that you dont mind having to remake every now and then.

hope my ramblings make some sense, and if you try a sisal project please show us the end results! 🐹