Hi Tema, it would probably help if you could show a picture of the piece you are working on. I have a little video on my website about how to crochet a border onto a knitted piece
if you would like to take a look at that. It might help you get started on your idea. Once you have done a single crochet border around the edge, then you can crochet pretty much any kind of design onto that.
Hope this helps.