Henrik, welcome to forum. What have you been trying?
The more or less standard when choosing a shooting head is to go up the equivalent of two line weights for the 30 foot head. For a seven weight rod, a regular 7 weight fly line would come in around 185 grains for the first 30 feet, with more line and more weight behind it to load the rod.
BUT, for a 30 foot shooting head on your 7 weight instead of a full fly line, you'd probably want to go up to 240 grains (+ or - 10 grains, equivalent to a 9 weight line) for a 7 weight rod.
I use 30 foot SH's on some rods in SW. On a 9 weight Sage RPLX and 10 weight RPLXi and use SH's that are 2 line weights heavier in grains than the line rating of the rod..
You'd want to match the head up with a running line. The easiest to handle would be a fly line type of running line specifically made for use with a running line, or a braided running line. Monofilament stuff like Amnesia might get you more distance and is less expensive, but it can be a pain since it has a tendency to blow all over the place and may cut your fingers if they're wet-- usually right in the joint where you bend your finger.
As you probably know, you can't false cast a shooting head with running line outside of the tip or the loop will collapse.
Here's a good article if you're thinking of making your own (out of inexpensive double taper fly line). Just don't get confused between GRAINS and GRAMS.
Shooting heads DIY - The more than Adequate Shooting Head DIY, a guide to building your own shooting heads for fly fishing - Global FlyFisher
Let us know what you've been trying and maybe some folks can weigh in