i'm the worst at directions so please forgive me, but here's my try at a better explanation on making this top.
the red is the stitich line, the blue numbers are the measurements that i made my top to (i'm about a medium to small) and the pink is the distance to the stitch- this distance will definitely depend on the stretchiness of your fabric though and you'll want the top tighter if your fabric is heavier.
*edit* oops! lets see if this makes it more understandable- the purple line on the left is the fold line, and the orange line on the right would be the selvages so from foldline to selvage measures 26 inches and the fabric is 20 inches wide. the 13 inches is the opening that your bust will be going through when wearing. the red line is the stitch line, i sewed mine 11 inches.
I also like to make a small dart like stitching on the inside of the folds of fabric just to make it lay better and more open. but it's not necessary.
and here's a pic of the top lying flat and with the afore-mentioned flower pin.
so, hopefully that helps. just let me know if you have any questions or if there's anything i didn't explain well.
and Please! post if you make one. i've only tried it in striped fabrics so i'd love to see some others.