I love to make my own fitted sheets and they are so easy to do. I get the right width material from http://www.fabric.com/ type in 108" and it will take you to the right page, there arent many color choices but with the right flat sheet and embroidery work, they come out looking wonderful. In fact I just finished a birthday sheet for a little boy that came out looking awesome.
Measurements you will need:
Length of mattress (L):
Width of mattress (M):
Depth of mattress (D):
For crib sheets add 4 inches and 8 inches for all other mattresses, this is what will tuck under the mattress. (for formula we will call this number T)
Now for the math
Length of fabric to cut fomula: L + (2 x D) + (2 x T).
Width of fabric to cut formula: W + (2 x D) + (2 x T).
Now to do the fun part. Making the sheet.
Cut fabric to your dimensions. At corner take out D+T, so if your number says 12 take 12 inch squares out of your corner, leaving you with 4 cut out squares, 1 from each corner.
Pin two sides of these squares together and sew. Leaving a point in place of the square hole you just cut out. Do this for all corners.
If you have one serge or zigzag stitch all sides of fitted sheet, just to make it nice and neat, also makes it look more professional.
Hem all sides with 1/2 inche seam.
Measure 8 inches in from corner to place elastic on long sides of sheet for crib sheets and 11 inches for all other sizes.
Thread elastic through hems, and zig zag stich while pulling it taut. Secure each end of elastic in place.
And now you are done. Put your new fitted sheet on your mattress and be amazed at the new thing you just made.
For your flat sheet, use the same measurements except at the head of the sheet make a 8 inches hem and 1/2 inch hem on all other sides, and now you a have sheet set.
If you want you can go the next step and make matching pillow cases. cut out a 30 x 40 rectangle, fold over and sew one long side and one short side. serge it if available. Make a 4 inch hem at the top and you are done.
Have fun ladies.