If you are learning to sew or want to hone your skills, I found this resource online. It's free and it shows you how to make your own patterns from your own measurements. There is an entire textbook that you can look through with patterns and methods from the 1900's to the 1950's. They show you how to make a sloper (sort of a paper guide based on your measurements), and from that how to design your own fashions. If I had a daughter, I would use this as a math credit for homeschooling. They even have tips on how to do your own dry cleaning.
http://www.vintagesewing.info/I also found these instructions on how to draft a 3, 5 and 7 gore skirt.
http://www.tudorlinks.com/treasury/freepatterns/w191214cdgoreskirt.htmlThe instructions are good, but I would add two items that they did not mention:
First, measure down from your waist to your hip. This may be from 7 to 12 inches, depending on your size. Then, measure around your hips at the widest part (tighten those cheeks

). When you are constructing your draft for your skirt, give enough room for your hip measurement. In other words, on the front panel, the waist measurement is 1/8 of your total waist measurement. Seven inches lower, there should be a horizontal line 1/8 of your total hip measurement. Repeat this on the side and back panels using 1/4 of your total hip measurement. Drawing a line down from the waist to the hip and following the angle out to the hem will give you enough room for movement at the hem.
Second, when determining the length of your skirt, measure from your waist to the floor. Have a measurement for the front, the side (from your waist, over the hip, to the floor) and the rear (from your waist over your bum to the floor). Once you have these three measurements, SUBTRACT the number of inches you wish your hemline to rise from the floor. So, if you are short and wish your skirt to fall just below the knee, you might want the hemline to rise 12(+/-) inches from the floor. A taller person may only wish to subtract 3 or 4 inches from the total length. This method allows the hemline to hang evenly (relative to the floor) all of the way around. This keeps the back from riding up if you must bend or stoop.
Are you saying to cut the back (or sides) longer than the front? If the measurement from your waist to the floor is longer in the back (or sides), yes. When you are wearing the garment, this allowance will make sure that your hem falls at the same place all of the way around.