I got a great book on how to do this. There are lots of posts on this topic which you can locate using search. I would either cut all one size or do all where the finished length/ width is a multiple of 3(when finished) such as 9.5x12.5 etc. cut the shirt apart very big, iron on a light stabilizer on the back and then cut to the useable size. Have fun. I have 3 that I have made and shirts cut to make 3 more. They also suggest a LAQ quilt it because of the material being difficult to work with on a domestic machine. I also found that buying a ruler that is the exact size to make the block. It makes "fussy cutting" them easier. A rotating mat makes it even easier although this is not be necessary.