has a good graphic on how to measure net and all. Thanks to HC4U!
One thing I feel is critical is the ridgeline. The rl maintains the proper distance so as not to stress the netting material. And you need to determine the rl distance before starting on your net, so the math works out. From there its just cut and sew.
If you want pockets or extras, just add the numbers up so your rl distance is right, and the perimeter of the net equals the total distance of the hammock fabric + seam allowances.
You can do a netted hammock without a rl, but the net will need to be looser (floppy).
Check the stickies at the start of each forum, they contain lots of valuable info.