I made this in a similar way to my Simple to sew jersey top . Here is a tutorial to sew your own Snuggly Sunday Sweatshirt, you will need to know how to insert a sleeve and sew a facing.
What you need:
Your favourite old sweatshirt
Heavy weight jersey fabric ( I used the lovely Mystique jersey fabric)
1.Lay your old sweatshirt onto your jersey fabric (folded in half so it is 2 layers thick) and fold in the arms
2.Cut carefully round 1 half of the sweatshirt, then remove the sweatshirt and fold the cut piece on top of the uncut half as use this as a template for the second half (doing this means that both sides of your sweater will be the same shape)
3.Lay one sleeve of your old sweatshirt along a folded piece of jersey fabric and cut round (do this twice, 1 for each arm)
4.Sew along the tops of the shoulders and down the sides, no need to finish the seems as jersey doesn't fray
5.Sew along the sleeve seem then insert the sleeves
7.To make the facing I traced the neckline and cut a 10cm deep facing. With right sides together I inserted that, finishing with a line of top stitching about 1cm from the edge.
8.To finish the sleeve I just rolled them up and added a couple of little stitches by hand to hold in place.
9.Again the hem can be just left but I fancied something a little more stylish so I added curved and slits in the edges. (You could also add a strip of ribbed trim, but I have found it really hard to find a supplier of ribbing)