Can anyone tell me which number tip will make a large shell border. I have never made one.

Thanks,

I have used tip 21, 32, 1M(also used for swirl on top of cupcakes) . I used the 1M on a very large tier.hth

I don't know how large you want, but any closed star tip
http://www.wilton.com/store/site/product.cfm?id=3E30C2D7-475A-BAC0-5CFE6A7765000D80&killnav=1
or open star tip
http://www.wilton.com/store/site/product.cfm?id=3E30DE4E-475A-BAC0-5286A221EFC16EC2&killnav=1
would work.

Squeeze harder for a bigger shell and do this:
http://www.wilton.com/technique/Shell

Thanks for the information. I will try those.