Is there a way to create your own custom skin and how?

If this is illegal then I did not know and I am sorry. So ever since I bought zed I always wanted to change his colors around but I could never figure out how. After a little snooping I came across a couple custom League skin websites such as LeagueCraft. However to my avail the skins aren't what I'd like so I am wondering if there is a way I could make my own skin. Instructions would be nice. Thanks