Fold your fabric in half - right sides together - and place the finished pair of sweatshorts on top and trace the shape. Cut this shape out. You now have one leg of your bottoms.
Take this leg and stitch up the long side and the crotch section. Do NOT stitch the bottom or the slop on the crotch side. The red lines in the photo indicate where you should sew.
Follow steps 1 & 2 to make the second leg of your pajama shorts/pants.
Turn one (1) leg right side out. Slide the right side out leg into the wrong side out leg. The crotch of both bottoms should be in the same direction and the right sides should be facing one another. Pin and place and stitch along the horse shoe shape that is still unstitched. Follow the red lines above.
Open your bottoms. They should look exactly like shorts/pants with rough edges. If the bottoms are stitched shut you did something wrong!
You are going to want to stitch the bottoms of the shorts. Try the bottoms on and deside how big the casing needs to be for the elastic. Make sure the bottoms sit where they are most comfortable. Stitch the casing and feed the elastic through!