alright, i'm going to do my best to explain this shirt - i'm sure it will be simple enough to recreate, or alter. but keep in mind, i find it terribly difficult to remember the process - it's kind of haphazard, just like me. you will need:
a pretty large t-shirt
less than a yard of cotton/whatever you'd like
1) cut the sleeves off the t-shirt. make sure you cut them the same, as they are going to be reincarnated as different sleeves.
2) with the remaining part of the t-shirt, cut horizontally across the main part of the shirt. this will become (surprise, surprise) the main body of the new shirt.
3) turn the tube of t-shirt fabric inside out and sew to the size of your body - i'm sure you all know how to do that.
4) for the cotton top of the shirt, you will need to measure your upper chest and cut the little U-shaped (well, vaguely at least) pieces. there really is no better way to explain it but to see what you like. just remember to add a seam allowance to your pieces and to cut two back and two fronts so you wont have raw edges. the back pieces should extend over the shoulder so there is room to sew the button on there.
5) with right sides together (18 years of sewing and i STILL do this wrong sometimes!) sew the U-shaped pieces together around the collar. you don't need to sew the ousides because they will be sewn to the black fabric, but if you'd prefer to, you'll have to change the math a little bit.
6) now, you take the tube, the two sleeves, the front and the back and pin them together. the sleeved (as you can see in the photo) are sewn to both the t-shirt and the polka-dots. it's pretty simple, since all you are doing is putting together the puzzle pieces.
7) to make the puff sleeves, I made a tiny cut in the edge stitching of the sleeve and threaded some thin elastic into it. I measured the elastic first to the size of my upper arm. don't make it smaller, or your arm will go numb. not so much fun to wear. the end of the sleeve should pucker because the sleeve circumfrence is bigger than that of the elastic. this creates the easiest puffy sleeves ever.
8 ) sew buttons to attach the back tab to the front tab at the shoulders. (see photo)
9) sew a long tube of fabric to use as the back tie. then sew the tie (under the arms) to the shirt to secure it at rib cage level.
and that's it - hopefully it is understandable? maybe i helped someone?
if anyone has questions, definitely ask me, cause i would love to see this top made by someone else.