I decided to do a simple pencil or straight skirt using an over-sized men's shirt I found at Wal-Mart for $5.
Step 1: Trace your skirt
Lay a straight skirt that fits you well on top. Make sure that the bottom of the skirt lines up with the bottom of your t-shirt. This way your skirt bottom will already be hemmed and finished.
Trace leaving a 1/2" seam allowance all the way around.
Step 2: Cut and sew
Sew up the side seams using 1/2" seam allowance.
Fold over the top of the skirt to the wrong side of skirt a hem of about 1- 1 1/2 ".
Sew this hem all the way around, leaving about 3" open.
Step 3: Insert Elastic
Make sure the elastic is not pulled to tight or too loose. You want it to fit snug enough to not fall off, but not too tight!
Add 1-2" to that measurement.
Insert elastic into casing you just made around the top of your skirt.
Over lap the elastic the 1-2" you added and sew the ends together.
Now close the casing up.