1.Grab some 1 to 2 yards of satin or flowy fabric, like polyester or silk which is what I’m using here. fold it in half to make a rectangle that is the length you want plus a few inches and the width to be at least as wide or wider as one of your boxiest tops. Make sure to incorporate the longer sleeves. Its always good to over estimate! Honestly If I had more fabric to work with I would have made it a little wider.
2.Mark around the top of the shoulders down to elbow length sleeves, making the sleeves wide and boxy like a rectangle .mark the shirt pretty wide if you can, At least 5 to 10 inches wider than a regular shirt. You can always take it in later. It will end up looking like so.
4.Sew up the side seams and the shoulder seams right sides together. Serge the edges if you like. Try the top on again and see if you need to make any adjustments.
5.Cut notches into the armpit corner or serge raw edges really close to the seam so the armpits don’t bunch after turning right side out.
6.Cut out two, two inch strips that are the length of the sleeve’s opening when folded, then sew the sort edges together right sides together to make a little tube.
7.fold it in half and pin the edges or the folded tube to the edge of the sleeve opening right sides together and sew close to the edge.
8.Fold the fabric inside the sleeve and pin it down concealing the new band you just sewed previous.
9.Then topstitched sleeve band down 3/4” in and right along the edge
10.Try the top on and mark and cut where you want the new neckline to be but make sure to add seam allowance. I did a simple rolled hem which is folding under 1/4” twice and sewing. But If I have enough material I would have loved to put in a neckline facing which would be preferable. I have a tutorial for a neckline facing in my youtube channel.
11.Hem the bottom by folding under 1/4” then 3/4” and sew along the 3/4” from the bottom to just get the fold sewn to the shirt. Then topstitch the edge as well which will end up matching the sleeve hem.