This parametric launch pad can be setup to hold any size rod with any size legs. I used it with 3/4" legs to hold a 1/4" launch rod. Buy some dowels for the legs, cut to whatever length you like, insert a launch rod, and put some sort of blast shield on, and you're good to go.

Note that this is a fairly light weight pad, so for heavy high-power rockets, you might want to add some sand bags or something to hold it steady.

This pad has been used to launch a variety of rockets up through level 1 high power successfully.