This web page will produce patterns for hemisphere parachutes for model rockets. Instructions for constructing the parachutes can be found in the May/June 2000 newsletter of the Northern Illinois Rocketry Association.
The article describes the construction of 12 inch diameter parachute with 8 gores and a 2 inch diameter spill hole. This web page will produce patterns for other sizes of parachutes. Patterns are limited to a size that will fit on an 8 1/2 x 11 inch sheet of paper.
As you are considering the size of your parachute, keep in mind that a spherical parachute has twice the drag coefficient of a comparable sized parasheet style parachute that comes with most model rocket kits.
Parachute shroud lines should be 1 1/2 times the diameter of the parachute.