First, you need to do some measuring. You will need 4 measurements.
1. Waist, you will want to measure around your stomach at your natural waist. My measurement was 28″. now you will want to take that measurement and divide by 6.28. this will give you your circumference. mine was 4.45. You can round this down a little bit to allow for fabric stretching. I made mine and even 4.25.
2. Length, you need to decide the length of your shirt. Measure from your waist to how long you want your shirt to be (if you are making a dress measure from your natural waist to how long you want the dress to be) I made mine 10″
3. Width of straps, to get the width of your straps, measure from your breastbone with your bra on, around the breast to the middle of your underarm. My measurement was 10″
4. Length of straps, your straps will need to be 1.5 times your height. I am 5’5″ which is 66″ so my strap length is 99″ I rounded it up to 100″.
Next cut a waistband 10″ tall and the length of your waist that you measured. Mine was 10″ by 28″. (If you would like a modesty panel built in you can just make the waistband longer so it will act as a tank top. If this is what you would like to do measure from where you want the modest panel to start in the front down to your natural waist. Use this measurement instead of the 10″.)
Now lay them on your skirt and place the middle of the overlapped straps on the skirt. This will now be the front middle of your shirt.
Pin the straps all the way around the circle. they should come around about halfway.
Sew the straps on.
Take your waistband and fold it in half. Start in the middle of the front of the dress and sew the waistband on, all the way around to the beginning. There should be just a little overlap.