You could look for a normal shirt pattern and leave out the sleeves. Hem it, rather than sewing the sleeves on? of couse you may have to cut a bit more of the fabric, so that the sleeve holes taper up to the collar (as i don't think miku has fabric over her shoulders?)
It's a little hard for me to write how to do it properly, so I might not me making much sense right now.
(I'm not 100% sure on this, you may want to see what other people have to say about it first)