I did this without a pattern, just because they confuse me, and I recommend having prior sewing experience before attempting this.

Also, I specifically made this for my little sister, using her size to measure everything.

Update:

After perfecting this dress, I recommend not doing step 2.4. In step 4

Supplies

1. Men's collared dress shirt (with sleeves)

2. Sewing machine

3. Sewing scissors

4. Pins

5. Measuring tape

6. 1/4" Elastic

7. A little sister willing to be a model

Step 1: Cutting the Main Figure

Lay the shirt out and have whoever it's being made for lay on top of it
Cut down the shirt on each side of the collar from where the person's shoulders are (the sleeves will be completely cut off)
Make a slight curve outward and continue down the shirt at a slant until the bottom of the shirt
Cut the sleeve about halfway and trim all the extra prior seams and the entire wrist and buttons off
Cut the remaining part of the lower sleeves in half and make sure they are the same size

Note: The upper part of the sleeves will be used for the ruffled sleeves, while the lower part of the sleeves will be used for hidden pockets.

Step 2: Pockets

Note: Use the lower part of the sleeves for this

Lay out 2 sets of pockets with 2 pieces in each set, all the same size
Pin the pockets on the outside of the dress on either side (shown above)
Sew each side of the pocket (x4) to the dress
Leave for later

Step 3: Ruffled Sleeves

Note: Use the upper part of the sleeves for this. The upper sleeve is supposed to be rounded on the top, so DO NOT CUT IT OFF (otherwise the sleeve with look like a tube and be very bunched underneath)

First, measure how long the sleeve will be, and cut off the extra (hem the bottom)
Second, measure the length around the person's upper arm and cut the 1/4" elastic to that length
Third, measure how far up the ruffle is wanted (from the bottom) and pin the elastic that far up on each side (there will be a big difference between the length of the elastic and the length of the sleeve, the more difference, the more ruffle)
Sew: first start sewing the elastic on just a little, then once it is secure, pull the elastic to match the length of the sleeve and sew the rest of it
Pin the arc of the sleeve to the midpoint of the shoulder
Determine how far down the sleeve should go, then sew up on each side, meeting at the pin and ruffling the extra fabric at the shoulder

Step 4: Finishing Sides

Turn inside-out and sew together from the bottom of the sleeve up to the armpit and then down, around the pocket (sewing it together in the process), to the bottom of the dress.