Fortunately, we have an extra twin-sized comforter that is nice and fluffy, but we weren't using because not only did the the color clash, but the fabric was discolored in some places. As we've been trying to stop spending money on home decor for this house, buying a new duvet cover or comforter wasn't an option. I've been sewing a lot lately and decided to sew a duvet cover that would match the room.
However, finding fabric wide enough for a duvet cover (without piecing it together) is not easy. Not to mention trying to do this as cheaply as possible. I found a plain gray twin-sized sheet set at Walmart for only $10, and though I knew I'd have a tight fit as the dimensions wouldn't give me any breathing room, I decided to try to make it work. In retrospect, the hardest part of this whole project was working with the twin-sized sheets...it would have definitely been easier to buy a sheet set that was a size larger, but Walmart was out of full-sized, and the queen-sized added another $10 to the price.
Sewing a duvet cover is not a hard task (there are plenty of people that have already written great, easy to follow tutorials online), but I didn't just want to use the sheets as they were, because I thought it'd look like a cheap giant pillow case. After looking up ideas online, I settled on the idea of using pintucks to add visual interest (and distract from the fact that it was made out of cheap bed sheets).
The width of a standard twin comforter is 63" and the width of the flat sheet (after pre-washing) was 61". With 1/2 inch seam allowances, the duvet cover would be about 3 inches too small. This wasn't really a drawback, though, because it would give the comforter a little more body instead of seeming flat around the edges.
After ripping the seam along the top edge of the sheet, I had about 12 inches of extra vertical length to use to make my tufts. I followed a tutorial I found online to make the pintucks, arranging them about 12 inches apart in each row, with rows spaced 6 inches apart. I laid the sheet out on the living room floor for this step, and it should be noted I do not recommend this project for women who are 8 months pregnant. :) After marking the location of each pintuck with safety pins, I started sewing the pintucks. I expected this part to take forever, but it actually went faster than measuring and marking the locations.
Finally I was ready to actually assemble the duvet cover! This part when quickly compared to the rest of the project. I lined up the edges of the top and bottom piece (the bottom piece was the fitted sheet with the elastic taken out and extra material sewn together to make it a perfect rectangle, but as it won't show, that didn't bother me), with right sides together. I sewed around three sides of the duvet cover, leaving the middle of the bottom edge open (to make the corners crisp on this fourth side, I recommend sewing about 8-10 inches on each side). I used pearl head snaps on the bottom edge, as they were easy to attach and look nice with the gray color.