Here is a tutorial on making a maxi dress from a close-fitting ribbed tee.
Sew the side seams first from the bottom up. Press. Now you will match up the side seams of the skirt with the shirt. Also pin at the centers. You will now stretch the shirt to match the skirt and sew. If you have a serger, this will be a breeze. There is no gathering stitches because the knit of the ribbed shirt will pull in the slight fullness of the skirt! Magic!
I make a rolled hem if I have matching thread and if I don't; I use a narrow turned hem-press 1/8" up and turn it and straight stitch it down. Very neat.
Press and wear! Enjoy!