I have seen this shirt floating around pinterest lately and thought it was really cute. While walking around the thrift store I found this big baggy men's shirt that was perfect for the job.
Step 1: Cut out the ribbing from around the neck, then hem the raw edges
Step 2: Cut off desired length and hem
Step 3: Take the extra fabric you cut from the length, and make a pocket shape
Step 4: Sew the pocket to the shirt, and sew your coat zipper directly on top of your pocket
Step 5: Roll the sleeves, then using the ribbing you cut from the neck, sew the ribbing ties around the rolls on the sleeves
Step 6: Your shirt is now ready to wear!
I went to the thrift store last week and found another shirt just like this one, so they are very easy to find. So go pick one up, and do some experiementing!