That looks like scaly leg mites to me. A bad case.
It is hard to get rid of.
A long used treaqtment is to make a mixture of one part kerosene to two parts linseed oil. Brush the mixture on roosts , perches and the chicken's legs. Repeat treatment every 10 days.
You can also give ivermectin. For bantams, 5-7 drops by mouth and for LF 1/4 cc by mouth.
It is very hard to get rid of and sometimes culling is best in severe infections. Even when they are gone, the raised scales may not return to normal. It will spread from bird to bird till controlled.