I was wondering if anyone has ever made one of there out of something and what size O-rings do you use?

I break open sharpie clickable markers and use them. I do not know the size of the o ring just ebay o ring for 5in senko and you should find a bunch for really cheap. 

Size O-Ring:  3/8OD 1/4ID

 

We discuss it in more detail on this thread

 

http://www.bassresource.com/bass-fishing-forums/topic/112106-wacky-rig-how-to-keep-the-worm-from-slipping-off-the-hook/

All I do is break off the clip on the cap of the sharpie then stick my sencos into the cap and slide the o rings on.

I don't use O-rings and never had a problem.  Too much hassle if you ask me.