In the bin that I made I used one single 'plank' of wood, initially it was smooth but I found out that Buster used it as a slide rather than a propper ramp
However I took a saw and cut shallow grooves (one stroke with the saw) in it to make grippy lines in it and he uses it fine now
I used bamboo skewers as well with jute string and stiff wire to make a 'ladder' (in the middle of the top-down second picture) as well.. worked fine but is now used as a walkway in his 'basement' on top of the woodchip to his sandbath