If you are using a standard running line, you can use standard shooting heads that are the same line weight as your rod, or up to 2 or 3 over, depending on the rod. If you want to make your own with LC-13 or TC-14 use this to get the right length: http://www.flyfishingforum.com/expertise/knowledge/lineratings.htm.

It is also possible to overload a rod and achieve good results, like I fish a 9 wt Rainshadow XCEL rod with a 400gr shooting head.

Now, as far as casting them, the heavier they are the more you should try to strive for one backcast. If you are having trouble with getting the cast started, try bringing the shooting head in the rod a foot or two and letting it out on the false cast. Its a good idea to learn to double haul, as that will help your line speed.

Rob