This skirt is created from a standard 8 gore skirt pattern. Copy your pattern onto cheap paper and remove the seam and hem allowances. You will be adding seam allowances after you create the diamond and cut the pattern pieces apart.
Now, measure the length of the side of your pattern piece, and divide that measurement by 4. Starting at the top, measure down that measurement, mark you pattern piece on both sides and draw a straight line between the marks.
(Figure 1)
(Figure 2)
Divide the remaining length of the pattern piece by 4. Measure down the sides from the bottom of the first line this amount, and make another set of marks. Draw another straight line across the pattern piece.
Mark the center of the hem edge of your pattern piece, draw straight lines from the second set of marks to this point. (Figure 3) 
You should now see the outline of your diamond.
(Figure 4)
Going back to the first straight line you drew, mark the center of this line. On the second line you drew, measure the length of the line, divide it into thirds and mark it. Draw lines from the corner of the top line to the first mark on the second line, from the center mark of the first line to both marks on the lower line, and from the second mark on the lower line to corner of the top line.
Draw lines from the marks on the lower line to the center mark at the hem edge. Your diamond is now complete. (Figure 5)
(Figure 6)
I add key marks to the lines drawn at this point for ease in assembly of the skirt.
Cut your pattern apart on the lines drawn and add seam allowances, or trace the individual pieces and add seam allowances. I prefer to trace the pieces and leave this pattern whole so I have a visual reference for assembly of the skirt. If you were accurate in your drawing, you will need a total of 8 pattern pieces for this skirt, including the waistband which we did not modify.
Diamond Skirt
Assembly Instructions
Pattern Pieces
# 1 - Upper yoke, Cut 8 
# 2 - Upper triangle, Cut 16
# 3 - Middle side triangle, Cut 16
# 4 - Middle center triangle, Cut 8
# 5 - Lower side triangle, Cut 16
# 6 - Lower center triangle, Cut 8
# 7 - Lower gore side piece, Cut 16
Waistband cut according to original pattern
All seams are finished by either serging, double stitching, or sealing edges with fray check. I prefer to serge seams with a narrow, 2 thread serge to reduce bulk. Stretchy fabrics should be stabilized with spray starch for ease in assembly.
Stitch 2 upper triangles, 2 middle side triangles, and 1 middle center triangle together, matching key marks, to create upper portion of diamond. Remember to press seams as you go. Repeat with remaining pieces to create 8 upper diamond pieces.
Stitch upper yoke pieces to top of upper diamond pieces to create 8 upper skirt pieces, set aside.
Stitch 1 lower side triangle to each side of lower center triangle, matching key marks, to create lower portion of diamond. Repeat with remaining pieces to create 8 lower diamond pieces.
Stitch 1 lower gore side piece to each side of lower diamond pieces to create 8 lower skirt pieces.
Stitch lower skirt pieces to upper skirt pieces, matching seams to create complete gores.
Stitch gores together into skirt, matching diamond seams. Stitch waistband to skirt top, insert elastic and finish waistband as desired. Hem skirt as desired with roll edge, piping, or lace.
A Prairie skirt can be made using the same instructions with the following modifications:
Determine the placement of the diamonds on the lower part of the skirt placing them at a visually pleasing distance from the waistband. The diamonds can be placed at the hemline, or at any visually pleasing height on the skirt gore. After determining the placement of the diamonds, draw the first line at the top of the diamond, if not placing them at the hemline, draw a line at the bottom of where the diamond will set, dividing the gore into 3 pieces. Then follow the directions to complete the diamond.
Put the gores together following the instructions to reconstruct the gores. Then finish your skirt in the usual manner.