Your best bet is to keep it simple. Most hamsters won't want to wear clothes, & will probably try to chew up the clothes. Just get an old t-shirt or sweat shirt (it will be soft & easy to work with). Cut it big enough to fit around your hammy, & about from the bottom of it's head to almost it's tail. Sew a casing (like a hem - fold fabric down & stitch, leaving enough space for elastic), string some thin elastic through - most sewing & craft stores sell elastic thread that would be perfect for this. Make sure the elastic is secure - either stitch it down or tie it together. The elastic should be big enough not to hurt hammy, but tight enough to keep clothes on. Try to put it over your hamster's head, like a dress or shirt. If this works, you could experiment with something more complicated. Or you could buy some of the clothes made for the 'Mazin Hamsters toys, & see if those would work. My daughter's & her friend's hamsters would chew those clothes to bits, stuff them in their cheek pouches, & try to turn them into part of their bedding, but I wish you luck anyway! Have fun.