What is a balloon Dress? (In a nut shell)
The balloon dress or balloon skirt is two garment in one, first you have a straight skirt and next you have a gather skirt, your straight skirt will be about one or two inches shorter than your gather skirt, you gather the bottom and top of the material for the gather skirt (waist and hem) then you sew your straight skirt on the inside of the gather skirt like a facing starting at the bottom and turn out pulling the bottom up giving it a balloon look.
How to make a balloon?
I make this Balloon dress for my daughter and lay out the instruction, first I make my Pattern from news paper, follow this link to make you basic  bodice pattern Foundation and this link for Fitted bodice drafting this link for skirt pattern.

The image below will show you how  to shade your pattern to get the top of this style.

Pattern Pieces
Raise your front and back bodice armhole about 1 inch and mark across. Mark strap as shown
to desire width. Blue shaded area show your Pattern pieces
Add 1-1/2 inch to the center back for button or zipper and ¾ inch seams all around (or place on your material and cut with seams and button allowance).
Center front is cut on fold

Sewing your balloon skirt:
Cut your gather shirt as show using desired measurement, for size 10 I use length 15 inch by 45 inches wide

Sew your straight skirt as normal leaving off the waist band and the hem,
(Straight skirt will act as a lining)
Join the back of your gather skirt leaving zip opening, gather top and bottom, (run two row gather thread for full gather look)

Join skirt sides be sure to get the hip measurement to the bottom or a measurement that will allow free walking space.
Join band for the skirt bottom and fit around the bottom of the gather, then fit the bottom of the straight skirt around on top the band turning the right side up, sew all three part around and turn out. (Follow picture instructions)

Sewing dress top: first join the shoulder straps at the shoulder and sew both sides, turn out and hem, attach straps to the to of your bodice front and back place the facing on top and sew, turn over and join the sides, sew darts.

This style has a built in waist band, sew waist band unto the skirt and join the top to the bottom.

Lots of styles from the 60th, 70th. and 80th are coming back  in this 21th Century, the balloon dress is one of those style

Pattern Layout

Cut four front and four back as pattern is fully lined.

join center front of dress and center front of lining

join side sean of dress and side seam of lining

sew dress strap and turn as shown

Tack strap to dress back both side, center back to located strap position
then place dress lining over dress and sew all around leaving bottom and position for the front strap open

clip and turn baste in place. sew and turn knot for the front.

sew knot as shown and front strap in place getting desired length.

Run gather stitch in skirt, gather pin to top and stitch all around leaving back open for a 12’’ to 18 inch zip (this will depend on the size dress you are making).

Pin and sew back zipper, sew and attach front bow as shown.